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By  "  xix 

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Univ.   of  Calif.  A£ric.  Expt.   Sta.  Bui.   504. 
Jan.   1919. 


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UNIVERSITY  OF   CALIFORNIA   PUBLICATIONS 


COLLEGE  OF  AGRICULTURE 

AGRICULTURAL  EXPERIMENT  STATION 
BERKELEY,  CALIFORNIA 


A  STUDY  OF  THE  EFFECTS  OF  FREEZES 
ON  CITRUS  IN  CALIFORNIA 

/ 

J  H.  J.  WEBBER  AND  OTHERS 

I.  A  STUDY  OF  THE  FREEZE  OF  1913  IN  CALIFORNIA 
By  C.  S.  MILLIKEN,  A.  R.  TYLOR,  W.  W.  BONNS,  and  H.  J.  WEBBER 

II.  CHANGES  THAT  TAKE  PLACE  IN  FROZEN  ORANGES 

AND  LEMONS 

By  E.  E.  THOMAS,  H.  D.  YOUNG,  and  C.  0.  SMITH 

III.  A  TEST  OF  THE  EFFICIENCY  OF  ORCHARD  HEATING 
By  A.  D.  SHAMEL,  L.  B.  SCOTT,  and  C.  S.  POMEROY 


BULLETIN  No.  304 

January,  1919 


UNIVERSITY   OF  CALIFORNIA  PRESS 

BERKELEY 

1919 


ArKORTiCDLf^RE 
.-M;F  rff'Aopfcitftn&  v. 


RFRKFI  FV     PAI 


BENJAMIN  IDE  WHEELER,  President  of  the  University. 

EXPEKIMENT  STATION  STAFF 

HEADS   OP   DIVISIONS 

THOMAS  FORSYTE  HUNT,  Director. 

EDWARD  J.  WICKSON,  Horticulture  (Emeritus). 

HERBERT  J.  WEBBER,  Director  Citrus  Experiment  Station;  Plant  Breeding. 

HUBERT  E.  VAN  NORMAN,  Vice-Director;  Dairy  Management. 

WILLIAM  A.  SETCHELL,  Botany. 

MYER  E.  JAFFA,  Nutrition. 

CHARLES  W.  WOODWORTH,  Entomology. 

EALPH  E.  SMITH,  Plant  Pathology. 

J.  ELIOT  COIT,  Citriculture. 

JOHN  W.  GILMORE,  Agronomy. 

CHARLES  F.  SHAW,  Soil  Technology. 

JOHN  W.  GREGG,  Landscape  Gardening  and  Floriculture. 

FREDERIC  T.  BIOLETTI,  Viticulture  and  Enology. 

WARREN  T.  CLARKE,  Agricultural  Extension. 

JOHN  S.  BURD,  Agricultural  Chemistry. 

CHARLES  B.  LIPMAN,  Soil  Chemistry  and  Bacteriology. 

CLARENCE  M.  HARING,  Veterinary  Science  and  Bacteriology. 

ERNEST  B.  BABCOCK,  Genetics. 

GORDON  H.  TRUE,  Animal  Husbandry. 

JAMES  T.  BARRETT,  Plant  Pathology. 

FRITZ  W.  WOLL,  Animal  Nutrition. 

WALTER  MULFORD,  Forestry. 

W.  P.  KELLEY,  Agricultural  Chemistry. 

H.  J.   QUAYLE,  Entomology. 

J.  B.  DAVIDSON,  Agricultural  Engineering. 

ELWOOD  MEAD,  Rural  Institutions. 

H.  S.  REED,  Plant  Physiology. 

J.  C.  WHITTEN,  Pomology. 

FRANK  ADAMS,  Irrigation  Investigations. 

C.  L.  ROADHOUSE,  Dairy  Industry. 

FREDERICK  L.  GRIFFEN,  Agricultural  Education. 

JOHN  E.  DOUGHERTY,  Poultry  Husbandry. 

S.  S.  ROGERS,  Olericulture. 

R.  S.  VAILE,  Orchard  Management. 

J.  G.  MOODEY,  Assistant  to  the  Director. 

Mrs.  D.  L.  BUNNELL,  Librarian. 


CITRUS  EXPERIMENT  STATION  STAFF 

HERBERT  J.  WEBBER,  Dean  and  Direc-  C.    O.    SMITH,    Instructor    in    Plant 

tor.  Pathology. 

J.    T.    BARRETT,   Professor   of   Plant  E   E   THOMAS;  instructor  in  Agricul- 

Pathology.  tural  Chemistry. 
W.  P.  KELLEY,  Professor  of  Agricul- 
tural Chemistry.  *•  •"-  PKIZER,  Superintendent  of  Cul- 
H.   J.    QUAYLE,   Professor    of   Ento-  tivations. 

mology.  H.    B.    FROST,    Instructor    in    Plant 

H.  S.  REED,  Professor  of  Plant  Physi-  Breeding. 

ology.  A.  F.  SWAIN,  Assistant  in  Entomol- 

H.  S.  FAWCETT,  Professor  of  Plant  ogy. 

Pathology.  F     F     HALMA>    Assistant    in    Plant 

L.  D.  BATCHELOR,  Professor  of  Plant  Physiology. 

Breeding. 

A     .  .      .    D     .              ,.  W.  D.  DREW.  Chief  Clerk. 
R.  S.  VAILE,  Assistant  Professor  ot 

Orchard  Management.  Mrs.  M.  J.  ABBOTT,  Librarian. 


A   STUDY  OF  THE   EFFECTS  OF  FREEZES 
ON   CITRUS   IN   CALIFORNIA* 

BY  H.  J.  WEBBER  AND  OTHERS 


CONTENTS 

PAGE 

INTRODUCTION 247 

I.  A  STUDY  OF  THE  FREEZE  OF  1913  IN  CALIFORNIA  BY  C.  S.  MILLIKE.V,  A.  R. 
TYLOR,  W.  W.  BONNS  AND  H.  J.  WEBBER 

Methods  of  investigation 249 

General  and  metcrological  observations 249 

The  effects  of  the  freeze  on  citrus  trees  and  fruits 255 

Effect  on  citrus  trees 255 

Effect  on  external  appearance  of  fruit 256 

Effect  on  internal  condition  of  fruit 257 

How  to  determine  the  extent  of  fruit  injury 258 

Effect  on  quality  and  uses  of  fruit 259 

Effect  on  foliage 259 

Effect  on  wood.  259 

Effect  on  bark 260 

Relative  hardiness  of  different  varieties  and  species  of  Citrus  fruits 261 

Relative  hardiness  of  trees 261 

Relative  hardiness  of  fruit 263 

Natural  factors  influencing  the  temperature 264 

Elevation 264 

Protective  hills 265 

Influence  of  canons 265 

Water  protection 265 

Protection  afforded  fruit  by  location  on  tree 265 

Artificial  methods  of  protecting  groves 266 

Windbreaks 266 

Effect  of  running  water  or  irrigating  during.freeze 267 

Effect  of  spraying  water  on  trees 268 

Effect  of  wrapping  trees 268 

Protection  by  lath  houses,  burlap  or  cloth  coverings 269 

Protection  by  artificial  heating 270 

Acreage  and  general  results 270 

Equipment  and  material 270 

Methods 273 

Temperature  at  which  to  fire.... 274 

Value  of  combined  effort '. 274 

Causes  of  failure 274 

Costs  of  heating 275 

*  Paper  No.  55,  University  of  California,  Graduate  School  of  Tropical  Agricul- 
ture and  Citrus  Experiment  Station,  Riverside,  Cal. 

210384 


246  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

PAGE 

Factors  influencing  resistance  of  trees  to  cold  injury.... 

Dormancy  of  trees 

Time  of  planting 

Dryness  

Irrigation 

Pruning 

Unhealthy  trees 

Influence  of  trunk  section  of  top- worked  trees.... 

Influence  of  roots  or  stocks 

Individuality  of  tree 

Treatment  of  frozen  trees 

Binding  loose  bark 

Waxing  and  painting  split  bark 

Pruning  injured  trees 

Removing  frozen  fruit 

Whitewashing  exposed  trunks 

The  renewal  of  badly  injured  young  trees 

Grafting  or  budding  badly  injured  trees 

Irrigation  to  aid  recovery  of  frozen  fruit 

Stimulating  growth  in  frozen  trees  by  fertilization.   . 

Treatment  of  wounds  on  frozen  trees 

After  effects  of  the  freeze 

Appearance  of  new  growth 

Dying  of  new  growth 

Blooming  and  fruiting  of  injured  trees 

Planting  frosted  nursery  trees 

Thawing  and  recovery  of  frozen  fruit 295 

The  sale  of  frozen  fruit 

Separation  of  good  fruit  from  frozen  fruit 296 

II.  CHANGES  THAT  TAKE  PLACE  IN  FROZEN  ORANGES  AND  LEMONS 
BY  E.  .E.  THOMAS,  H.  D.  YOUNG  AND  C.  O.  SMITH 

Specific  gravity  of  fruits 

Specific  gravity  of  juice 

Sugar  content 

Acid  content 

Growth  of  frozen  fruit 

Summary 312 

III.  A  TEST  OF  THE  EFFICIENCY  OF  ORCHARD  HEATING 

BY  A.  D.  SHAMEL.  L.  B.  SCOTT  AND  C.  S.  POMEROY 
A  test  of  the  efficiency  of  orchard  heating 315 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  247 


INTRODUCTION 

The  recent  injury  to  the  citrus  industry  caused  by  the  severe  cold 
weather  of  the  first  week  in  January,  1919,  has  again  emphasized  the 
importance  of  having  available  for  the  use  of  growers  data  on  the 
effects  of  such  freezes  as  a  guide  in  handling  injured  fruit  and  trees. 
Following  the  great  freeze  of  January  5  to  7,  1913,  a  frost  damage 
survey  was  organized  by  the  College  of  Agriculture  under  the  direc- 
tion of  the  Citrus  Experiment  Station  and  much  valuable  material  was 
collected.  This  information. has  been  summarized  and  is  published 
in  this  bulletin  with  the  belief  that  it  will  be  of  service  to  growers  in 
handling  the  problems  connected  with  this  winter's  freeze. 

Much  of  the  data  presented  and  the  methods  suggested  are  appli- 
cable to  any  freeze,  but  some  of  the  matter  presented  has  historical 
value  only.  The  section  on  "Protection  by  Artificial  Heating"  will 
be  recognized  as  not  being  up  to  date.  Even  this  section  of  the  bulletin, 
however,  is  believed  to  be  of  value,  as  it  is  a  record  of  achievement 
in  the  "big  freezes"  with  what  would  now  be  considered  very  inferior 
equipment.  If  growers  succeeded  so  well  with  inferior  equipment  it 
would  seem  certain  that  a  grove,  with  modern  equipment,  could  be 
perfectly  protected  in  another  freeze  of  equal  severity.  To  delay  the 
publication  until  such  sections  could  be  brought  thoroughly  up  to 
date  would  make  its  publication  too  late  to  be  of  any  serivce  in  the 
present  freeze. 

This  bulletin,  then,  is  really  a  record  of  the  freeze  of  1913.  While 
there  had  been  freezes  in  preceding  years,  in  which  citrus  fruits  and 
various  subtropical  plants  were  somewhat  injured,  nothing  so  severe 
and  disastrous  as  this  freeze  had  occurred  in  the  state  since  the  citrus 
industry  was  started. 

Aside  from  the  general  field  studies  and  observations,  special  studies 
were  made  on  the  chemical  and  physical  changes  that  took  place  in  the 
deterioration  of  frozen  fruits.  It  is  the  purpose  of  this  bulletin  to 
discuss  such  of  the  studies  as  it  is  thought  will  be  of  interest  and  value 
to  growers,  in  case  of  future  freezes.  No  attempt  will  be  made  to 
compare  the  relative  degree  of  damage  done  to  groves  in  various  sec- 
tions, as  it  is  thought  that  the  conditions  shown  in  this  freeze  might 
be  reversed  or  much  changed  in  another  freeze,  and  such  comparisons 
might  thus  be  misleading. 

Messrs.  A.  D.  Shamel,  L.  B.  Scott,  and  C.  S.  Pomeroy,  of  the  U.  S. 
Department  of  Agriculture,  cooperated  with  the  Experiment  Station 


248 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


in  making  certain  observations  on  the  effectiveness  of  artificial  heating, 
and  their  findings  are  reported  in  a  special  article  in  this  bulletin. 

Many  growers  in  various  parts  of  the  state,  too  numerous  to 
mention  individually,  have  also  greatly  assisted  our  investigators  and 
have  given  freely  of  their  time  and  experience.  To  these  and  to  all 
who  have  aided  in  the  preparation  of  this  report  I  wish  to  express  the 
thanks  of  the  institution. 

H.  J.  WEBBER, 

Director,  Citrus  Experiment  Station. 


Fig.  1. — Badly  frozen  Eureka  lemon  grove.  Leaves  still  hanging  but 
drying  out.  Photographed  by  Smith,  March  7,  1913.  (See  same  grove 
later  in  fig.  2.) 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  249 


A  STUDY  OF  THE  FREEZE  OF  1913  IN  CALIFORNIA 
BY  C.  S.  MILLIKEN,  A.  R.  TYLOR,  W.  W.  BONNS,  AND  H.  J.  WEBBER 

METHODS  OF  INVESTIGATION 

In  gathering  the  data  for  this  report  a  large  number  of  the  citrus 
groves  in  different  districts  of  southern  California  were  visited. 

In  making  the  observations  several  trips  were  necessitated  to 
various  sections  in  order  to  determine  the  final  effects  of  different 
methods  of  treatment.  Wherever  an  interesting  case  or  experiment 
was  found,  the  observer  continued  to  follow  the  recovery  of  the  trees 
until  the  full  effect  of  the  treatment  became  apparent.  One  of  the 
writers  of  this  article  made  similar  extended  observations  following 
the  great  freeze  of  1894—95  in  Florida*  and  in  this  article  frequently 
a  comparison  of  the  conditions  and  methods  of  treatment  has  been 
made. 

The  conclusions  which  have  been  drawn  are  based  upon  numerous 
observations,  and  these  have  been  made  in  a  number  of  different 
districts  by  many  different  observers.  While  it  is  possible  to  find 
exceptions  to  most  rules,  the  value  of  the  rules  is  not  destroyed  by  the 
exceptions,  and  so  in  this  summary  of  the  effects  of  the  freeze,  an 
attempt  has  been  made  to  state  those  things  which  as  a  rule  were  found 
to  prevail,  believing  that  the  clearest  record  of  conditions  can  be  given 
in  this  way. 

GENERAL  AND  METEOROLOGICAL  OBSERVATIONS 

The  freeze  began  Sunday,  January  5,  1913.  Unlike  visitations 
from  frost  in  previous  years,  the  Sunday  cold  was  accompanied  by  a 
strong  wind.  Somewhat  different  conditions  prevailed  in  different 
places.  The  following  are  the  conditions  as  noted  at  the  Citrus  Experi- 
ment Station.  Sunday,  January  5,  was  a  cold  day  throughout.  Ice 
three-sixteenths  of  an  inch  thick  was  observed  in  the  street  about 
noon,  toward  evening  the  wind  went  down,  and  between  7  P.M.  and 
11 :30  P.M.,  the  coldest  period,  there  was  scarcely  any  movement  of  air. 
The  temperature  during  this  period,  at  a  point  about  300  feet  to 
the  east  of  the  grove,  remained  between  15°  and  18°  F.  (Compare 
Chart  I). 


*  Webber,  H.  J.,  The  Two  Freezes  of  1894-95  in  Florida,  and  What   They 
Teach,  Yearbook,  U.  S.  Dept.  Agr.,  1895,  pp.  159-174. 


250 


UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 


__•    OJ 


H  3 

3    —~ 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  251 

In  general  throughout  the  citrus  belt  the  Sunday  night  cold  was 
accompanied  by  a  strong  wind  that  blew  throughout  the  night.  By 
Monday  night,  January  6,  the  wind  had  died  down,  but  the  cold  was 
unabated;  and  on  Monday  night  and  Tuesday  morning  the  tempera- 
ture went  lower  than  it  had  gone  the  night  before.  Tuesday  night 
and  Wednesday  morning  were  also  cold,  sufficiently  so  in  most  of  the 
citrus  districts  to  freeze  fruit.  After  this,  the  temperature  became 
more  moderate,  although  for  several  days  the  skies  were  cloudy  and 
the  weather  stayed  cool.  On  the  9th  and  10th,  there  were  light  rains 
in  most  sections  and  heavier  rains  about  the  middle  of  the  month. 
The  month  of  January  as  a  whole  was  the  coldest  January  for  fifteen 
years;  while  the  cold  spell  from  the  5th  to  the  8th  was  the  coldest 
weather  ever  experienced  by  citrus  growers  in  southern  California. 

Heretofore  cold  spells  have  usually,  occurred  on  still,  cloudless 
nights.  On  such  nights  the  air  becomes  stratified,  the  colder  strata 
resting  on  the  ground.  A  breeze  improves  the  temperatures  at  such 
times  by  mixing  the  strata  of  warm  air  with  those  of  colder  air.  The 
freeze  of  1913,  however,  was  very  different  from  previous  periods  of 
cold.  It  was  preceded  by  strong  winds  which  came  from  the  north- 
west and  north.  Mr.  A.  G.  McAdie,  of  the  United  States  Weather 
Bureau,  has  called  attention  to  the  fact  that  the  winds  preceding 
frosts  in  California  usually  come  from  the  northeast.  He  points  out 
that  this  year  the  cold  wind  came  from  the  north  and  northwest, 
moving  directly  over  the  Sierra  Madre  Mountains,  with  their  elevation 
of  six  thousand  feet,  instead  of  taking  the  customary  course  through 
the  El  Cajon  Pass. 

The  temperature  records  reported  from  various  places  are  in  gen- 
eral so  inaccurate  that  little  dependence  can  be  placed  upon  them. 
The  Weather  Bureau  records  are  thus  the  best  ones  that  can  be 
taken  for  comparison.  True,  these  records  do  not  represent  grove 
records,  but  they  are  at  least  comparative  for  different  places.  The 
following  table  supplied  by  Dr.  Ford  A.  Carpenter,  in  charge  of  the 
Los  Angeles  Observatory,  U.  S.  Department  of  Agriculture,  Weather 
Bureau,  gives  the  maximum  and  minimum  records  for  the  period  of 
the  freeze  for  various  points  in  California. 

The  minimum  temperatures  reported  from  the  different  parts  of 
southern  California  show  a  range  from  25°  F.  to  — 2°  F.  The  accu- 
racy of  these  extremes  may  well  be  questioned.  It  may  safely  be 
concluded  that  most  citrus  districts  reached  a  temperature  as  low  as 
18°  F.  Several  places  have  reliable  records  as  low  as  15°  F.,  and  a 
few  places  show  apparently  reliable  records  as  low  as  12°  F.  In  many 
sections  the  temperature  remained  at  or  below  freezing  for  sixty 
hours. 


252  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

TABLE  1. — MINIMUM  AND  MAXIMUM  TEMPERATURES,  JANUARY  5-7,  1913,  IN 
VARIOUS  PARTS  OP  CALIFORNIA 

Minimum  temperature  Maximum  temperature 


Stations  5th  6th  7th  5th  6th  7th 

Azusa    25  22  20  48  49  54 

Bakersfield  28  16  14  52  49  40 

*Beaumont  20  16  24  25  32  38 

»Chino  30  28  16  44  42  44 

Claremont  27  25  19  47  42  49 

•Colton   28  27  19  42  35  47 

*Duarte  28  28  ....  45  46 

El  Cajon  30  20  21  52  46  54 

Escondido  32  15  13  56  42  45 

•Exeter  17  17  19  54  52  51 

Fresno     24  17  20  39  39  44 

Lemon  Cove  22  18  20  65  52  56 

Los  Angeles  36         '    30  28  49  47  50 

Monrovia    28  24  18  50  45  50 

Pasadena 31  25  21  47  43  50 

Pomona  25  21  18  48  43  51 

Porterville    22  20  18  41  46  48 

Eedlands  31  22  18  42  36  50 

Biverside  30  21  22  48  41  55 

San  Bernardino  31  26  18  46  35  53 

San  Diego  36  28  25  47  45  49 

Three  Bivers  28  17  16  40  39  44 

Ojai  Valley  J 28  13  13  49  50  55 

Santa  Barbara 28  27  30  52  44  58 

*Tustin  (Irvine 

Eanch)    48  32  34  70  50  56 

At  stations  marked  (*)  the  minimum  temperatures  were  taken  at  7  A.M.,  and 
are  probably  not  so  low  as  the  true  minimum.  The  maximum  records  of  these 
stations  were  taken  at  2  P.M.,  and  are  probably  lower  than  the  true  maximum. 

Frosts  during  the  winter  months  are  not  uncommon  in  southern 
California,  and  it  often  happens  that  a  certain  amount  of  loss  of  fruit 
results  from  low  temperatures,  especially  in  low  places  where  the 
citrus  area  has  been  extended  out  beyond  its  adaptable  sphere.  Abbot 
Kinney  in  his  book  on  Eucalyptus  refers  to  an  unprecedented  frost 
in  1893.  In  1898  in  certain  sections,  severe  damage  was  experienced, 
and  again  in  December,  1912,  a  very  heavy  frost  occurred,  but  the 
freeze  of  January,  1913,  was  probably  more  severe  and  widespread 
than  any  ever  experienced  here  within  the  memory  of  white  man. 

Maximum  and  minimum  thermometers,  although  of  much  greater 
value  and  satisfaction  than  the  ordinary  instruments,  are  in  them- 
selves of  little  real  value,  unless  it  is  possible  to  compare  these  recorded 
temperatures  with  the  story  as  pictured  by  thermograph  records  taken 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA 


253 


in  the  same  vicinity,  for  the  actual  minimum  temperature  means  but 
little  in  regard  to  the  resulting  effects  upon  plant  life,  unless  the  dura- 
tion of  the  low  temperature,  as  well  as  the  actual  minimum,  is  also 
known.  Lemon  trees  subjected  to  a  temperature  of  20°  to  22°,  but 
of  very  short  duration,  were  not  injured ;  while  the  much  more  hardy 
orange  trees,  experiencing  a  similar  low  temperature  that  continued 
for  nine  or  ten  hours  on  three  successive  nights,  were  entirely 
defoliated. 


Fig.  2. — Badly  frozen  Eureka  lemon  grove  two  months  after  the  freeze. 
The  same  trees  as  those  shown  in  fig.  1,  but  three  months  later.  Photo 
by  Smith,  June  24,  1913. 

The  elevation  of  groves  above  sea-level  does  not  indicate  their 
liability  to  frost  injury.  Citrus  fruits  in  southern  California  are 
grown  at  elevations  ranging  from  sea-level  to  twenty-seven  hundred 
feet  or  more;  and  while  in  some  sections  trees  at  sea-level  suffered 
severely  from  the  January  freeze,  and  groves  at  1400  and  1500  feet 
were  unharmed,  in  other  sections  the  reverse  conditions  occurred. 


254  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 


Fig.  3.— Frozen  Valencia  oranges  showing  characteristic  spots  on  surface 
and  the  breaking  down  of  the  interior,  accompanied  by  thickening  of  the 
skin.  Photo  by  Smith. 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA 


255 


THE  EFFECTS  OF  THE  FREEZE  ON  CITRUS  TREES  AND  FRUITS 

Effect  an  Citrus  Trees. — One  of  the  first  noticeable  effects  of  the 
cold  weather  upon  citrus  trees  was  the  formation  of  ice  in  the  fruits. 
The  ice  formed  earlier  in  lemons  than  in  oranges,  and  at  the  same 
temperature  lemon  fruits  were  frozen  much  firmer  than  oranges.  At 


Fig.    4.  —  Lemons   showing   characteristic    external    spotting    of    fruit    and 
breaking  down  of  tissues  caused  by  freezing.     Photo  by  Smith. 

temperatures  at  which  lemons  were  frozen  so  that  they  were  solid, 
juiceless  and  brittle,  oranges  could  be  pressed  out  of  their  natural 
shape  and  some  juice  could  be  extracted. 

Another  effect  of  the  low  temperature  which  made  a  conspicuous 
change  in  the  appearance  of  the  trees  was  the  curling  of  the  leaves 
of  the  orange  trees  during  the  cold.  This  curling  of  the  leaves,  which 
did  not  occur  on  the  lemon  trees,  gave  to  the  orange  trees  a  sort  of 
deathly  aspect.  It  was  commonly  remarked  by  growers  that  the 
orange  trees  seemed  to  be  affected  worse  than  the  lemons,  and  many 

DIVISION  OF  SUBTROPICAL  HORTICULTURE 
COLLEGE  OF  AGRICULTURE 


nrni/ri  cv 


ICftDNIA 


256  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

growers  were  prepared  to  believe  that  another  of  the  unusual  things 
so  usual  in  California  had  happened  and  that  lemon  trees  had  been 
less  injured  than  orange  trees  by  the  cold.  In  a  few  days,  however, 
the  leaves  of  the  lemon  trees  began  to  droop  and  turn  brown;  while 
the  orange  leaves,  where  the  temperature  did  not  go  too  low,  unrolled 
and  assumed  their  normal  functions.  Due  to  the  slow  physiological 
changes  in  both  fruit,  foliage  and  wood  following  the  freeze,  it  was 
some  time  before  accurate  indications  of  the  extent  of  damage  became 
visible. 

Effect  on  External  Appearance  of  Fruit. — The  orange  and  lemon 
fruits,  while  still  frozen,  often  showed  in  the  skin  clear,  icy  areas 
adjoining  other  areas  which  were  not  icy.  A  few  days  after  the  freeze 
these  fruits  became  spotted  (figs.  3  and  4),  caused  by  a  shrinking  of 
the  tissue  between  the  oil-bearing  cells  and  a  consequent  drawing 
together  of  these  more  deeply-colored,  oily  portions  of  the  skin.  Soon 
after  the  freeze  lemons  which  were  frozen  very  hard  were  covered 
with  white  watery  patches,  which  gave  them  a  loathsome  appearance. 
A  black  mold  frequently  established  itself  on  these  fruits  and  they 
shriveled  and  dried  up  on  the  trees. 

The  degree  to  which  fruit  becomes  spotted  gives  a  good,  early 
indication  of  the  severity  with  which  it  is  damaged,  especially  with 
oranges.  If  none  of  the  oranges  in  a  grove  are  spotted,  the  fruit  may 
have  been  injured,  but  usually  there  still  will  be  fruit  of  value  in  the 
grove.  Where  the  freezing  has  been  harder,  spotted  fruit  will  show 
on  the  north  side  of  the  tree,  and  to  some  extent,  there  will  be  spotting 
on  the  north  side  of  fruit  on  the  south  side  of  the  tree.  The  stem 
end  seems  to  be  most  easily  spotted.  In  groves  where  north  side 
spotting  is  general,  there  is  little  fruit  which  will  not  show  signs  of 
deterioration  by  the  time  three  months  have  passed.  The  fruit  which 
is  spotted  is  valueless,  for  though  it  may  retain  juice  for  some  time, 
it  deteriorates  so  rapidly  that  it  does  not  pay  to  ship  it.  Where  the 
fruit  in  all  parts  of  the  tree  is  spotted,  but  little  value  can  be  attached 
to  the  crop. 

All  citrus  fruits  are  not  subject  in  the  same  degree  to  this  frost 
spotting.  The  tangerine  apparently  is  not  subject  to  it  and  the 
Valencia,  while  sometimes  found  badly  marked,  is  much  less  suscep- 
tible than  either  the  navel  or  the  Ruby  Blood.  Both  the  pomelo  and 
lemon  are  readily  marked  with  these  frost  spots,  the  former  fruit, 
when  exposed,  being  especially  susceptible.  The  frost  spots  of  both 
the  pomelo  and  lemon  in  time  turn  brown  and  become  far  more  con- 
spicuous on  the  yellow  background  of  these  fruits  than  the  yellow 
spots  of  the  orange  on  the  orange-colored  background  of  that  fruit. 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA 

Effect  on  Internal  Condition  of  Frozen  Fruit. — One  of  the  earliest 
internal  indications  of  frost  damage  in  citrus  fruits  is  the  formation 
in  the  membranes  or  pulp  of  small  white  spots  or  crystals  of  hesperidin. 
In  oranges,  lemons  and  grapt  fruit  these  are  found  on  the  membranes 
between  the  segments  (fig.  5).  In  tangerines  where  they  are  very  con- 
spicuous they  are  scattered  throughout  the  pulp.  These  white  spots 


Fig.  5. — White  spots,  hesperidin  crystals  formed  in  the  membranes  of 
the  Washington  Navel  orange  as  a  result  of  freezing.  One  of  the  most 
characteristic  symptoms  of  cold  injury.  Photo  by  Smith,  February  8,  1913. 
(Somewhat  enlarged.) 

can  be  found  in  from  five  to  ten  days  after  the  freezing  and  can  best 
be  seen  by  cutting  the  fruit  transversely  and  tearing  the  segments 
apart. 

When  frozen  oranges  are  cut  transversely  they  often  show  a  pale 
area  part  way  between  the  center  of  the  fruit  and  the  skin.  Frozen 
lemons  are  somewhat  more  opaque  than  uninjured  fruit.  .In  all  varie- 
ties the  pulp  cells  of  frosted  fruit  tear  apart  more  easily  when  cut 
across  than  is  the  case  with  unfrozen  fruit. 


258  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

When  a  month  or  so  has  elapsed  after  the  freezing,  the  segments 
of  fruit  begin  to  pull  apart  because  of  the  drying  of  the  frozen  tissue 
(figs.  3  and  4).  This  condition  is  best  seen  in  cross-section.  It  shows 
first  in  fruit  which  was  exposed  to  the  morning  sun  where  it  may 
appear  within  ten  days  after  the  freezing.  Sometimes,  especially  with 
fruit  inside  the  tree,  this  breaking  down  may  not  begin  for  three 
months. 

How  to  Determine  the  Extent  of  Fruit  Injury. — It  is  frequently 
of  importance  soon  after  a  freeze  to  be  able  to  determine  the  extent 
of  the  fruit  injury.  The  external  and  internal  character  shown  by 
frozen  fruit  are  given  in  the  preceding  sections. 

Another  method  of  recognizing  fairly  quickly  the  good  from  the 
frozen  fruit  was  found  in  the  changes  in  specific  gravity  that  took 
place  in  fruits  that  were  picked  and  stored.  Good  fruit  increases  in 
specific  gravity  by  the  drying  out  of  the  skin  causing  a  decrease  in 
volume  without  much  loss  of  the  interior  juices.  Frozen  fruit,  how- 
ever, rapidly  decreases  in  specific  gravity  as  the  interior  juices  pass 
out  into  the  skin  readily,  and  are  evaporated  without  producing  much 
change  in  volume. 

In  an  investigation  conducted  by  Professor  John  S.  Burd  and  Mr. 
W.  H.  Dore  of  the  College  of  Agriculture  it  was  found  that  these 
changes  could  be  greatly  hastened  by  picking  and  storing  the  fruit 
in  a  warm  atmosphere.  The  following  statements  prepared  by  them 
will  show  the  possibilities  of  this  method. 


The  following  typical  data  illustrate  the  relative  changes  in  specific  gravity 
of  unfrozen  and  frozen  fruit  over  several  time  intervals  when  stored  in  a  cool 
room.  The  figures  in  every  case  represent  the  average  of  a  number  of  individuals. 

FRUIT  STORED  IN  COOL  BOOM 

After  After  After 

Initial          4  days          8  days         16  days 

Unfrozen  oranges  0.857  0.865  0.876  0.894  Maximum  50  days  0.951 

Frozen  oranges  0.838  0.836  0.828  0.787  After  40  days  0.689 

Unfrozen  lemons  0.942  0.955  0.967  0.981  Maximum  50  days  1.023 

Frozen  lemons  0.806  0.747  0.615 

When  sound  and  frozen  fruit  are  stored  in  a  room  at  a  temperature  of  95°  F., 
the  specific  gravity  changes  are  similar  in  character  to  those  observed  in  the  cold 
room  fruit,  but  the  rate  of  change  is  about  three  times  as  great  in  the  warm  room 
as  in  the  cold,  as  shown  in  the  following  data. 


DIVISION  OF  SUBTROPICAL  HORTICULTURE 

COLLEGE  OF  AGRICULTURE 

BERKELEY,  CALIFORNIA 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  259 

FRUIT  STORED  IN  WARM  ROOM 

After  After  After 

Initial  4  days  8  days  16  days 

Unfrozen  oranges  0.848  0.874  0.920  0.926   (Maximum) 

Frozen  oranges  0.842  0.842  0.816  0.729 

Unfrozen  lemons  0.943  0.979  1.006  (Maximum) 

Frozen  lemons  0.811  0.691 

The  absence  of  change  in  the  first  interval  in  the  case  of  the  frozen  oranges 
is  due  to  the  fact  that  a  gain  in  specific  gravity  in  some  individuals  counter- 
balanced a  corresponding  loss  in  others.  After  the  first  four  days  nearly  all 
individuals  showed  a  decrease. 

By  picking  separately  a  quantity  of  fruit  from  different  parts 
of  an  injured  grove  and  different  parts  of  certain  trees,  and  storing 
it  in  a  warm  dry  room  at  a  temperature  of  from  85°  to  100°  F.  within 
six  to  ten  days  the  changes  have  become  marked  and  an  examination 
will  enable  an  accurate  estimate  to  be  made  of  the  damage. 

Effect  on  Quality  and  Uses  of  the  Fruit. — Oranges  that  were  frozen 
sometimes  developed  a  bitter  taste  after  the  freeze.  This,  however, 
was  by  no  means  universal,  and  later  this  bitterness  disappeared. 
Even  when  no  bitterness  was  produced  the  flavor  was  affected,  becom- 
ing gradually  less  rich.  No  harmful  ingredients  developed,  however, 
and  the  oranges  were  very  generally  eaten  so  long  as  they  remained 
juicy  and  palatable.  So  much  was  said  immediately  after  the  freeze 
regarding  the  possible  injury  to  health  that  might  result  from  the 
eating  of  frozen  fruit  that  this  point  should  be  strongly  emphasized. 
In  California  and  Florida  and  indeed  in  practically  every  orange 
country,  frozen  fruits  have  from  time  to  time  been  used  in  large  quan- 
tities without  injury.  The  evidence  on  this  matter  is  so  extensive 
that  we  may  conclude,  without  fear  of  contradiction,  that  under  all 
ordinary  conditions  frozen  fruit  may  be  eaten  with  the  same  impunity 
as  normal,  unfrozen  fruit.  So  long  as  the  frozen  oranges  remain  juicy 
and  palatable  they  may  be  considered  as  a  wholesome  article  of  food. 

Effect  on  Foliage. — The  fruit  of  citrus  trees  is  more  tender  than 
other  parts  of  the  trees  with  the  exception  of  the  tender  young  growth 
(fig.  6).  Next  to  the  fruit  in  tenderness  are  the  leaves  and  then  the 
wood.  There  were  areas  during  this  freeze  where  all  of  the  fruit  on 
lemon  trees  was  frozen  and  the  trees  still  retained  50  per  cent  or  more 
of  their  foliage.  Many  acres  of  orange  groves  had  all  of  the  fruit 
frozen  without  any  loss  of  matured  foliage. 

Effect  on  Wood. — Young  trees,  of  course,  suffered  more  than  older 
trees,  and  young  parts  of  trees  more  than  older  parts  (fig.  6).  The 
parts  of  the  bearing  trees  that  had  been  of  faster  growth  were  injured 


260 


UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 


much  more  readily  than  the  parts  of  the  trees  that  had  attained  their 
size  more  slowly.  This  is  probably  the  explanation  of  some  of  the 
freakishness  noticed  in  trees  where  one  branch  of  the  tree  was  killed 
and  the  rest  of  the  tree  remained  undamaged. 

A  case  illustrating  this  point  may  be  cited,  where  a  navel  orange 
tree  showed  no  signs  of  injury  except  on  one  branch,  and  this  branch 
was  killed.  On  careful  inquiry,  it  was  found  that  a  year  or  two  before 


Fig.  6. — Valencia  orange  tree  in  foreground  on  which  the  young  rapidly 
growing  branches  were  all  killed.  The  mature  foliage  on  the  older  trees 
in  the  background  was  but  slightly  injured.  The  fruit  on  trees  showing 
such  injury  is  certain  to  be  a  total  loss.  Photo  by  Smith,  January  24,  1913. 

a  branch  on  this  side  of  the  tree,  which  was  particularly  heavy  with 
fruit,  was  twisted  and  broken  during  a  strong  wind,  so  that  it  had  to 
be  cut  out,  leaving  a  large  hole  in  the  side  of  the  tree.  A  new  sprout 
grew  out  near  the  base  of  the  cut  branch,  and  it  was  this  rapidly- 
grown  branch  that  was  frozen. 

Effect  on  Bark. — After  the  freeze,  many  of  the  trees  showed  a 
splitting  and  loosening  of  the  bark.  This  was  especially  common  on 
lemon  trees,  but  occurred  also  on  orange  and  grapefruit  trees,  where 
the  temperature  went  sufficiently  low.  Sometimes  the  bark  split  even 
when  the  foliage  was  not  damaged,  and  cases  were  reported  where  the 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  261 

bark  on  limbs  had  been  split,  and  the  fruit  on  these  limbs  had  not  been 
noticeably  injured. 

The  loosening  of  the  bark  in  most  cases  signified  the  killing  of  the 
cambium  layer,  but  this  was  not  always  the  case,  because  several 
months  after  the  freeze,  it  was  common  to  find  bark,  which  had 
loosened  along  one  edge  but  which  had  continued  to  live  and  grow, 
forming  a  new  layer  of  wood  (fig.  11).  One  tree  was  found  where  a 
strip  of  bark  had  completely  separated  from  the  tree,  forming  a  bridge. 
The  bark  was  alive  and  had  developed  a  layer  of  wood  and  a  new 
bark  had  formed  next  to  the  tree. 

The  most  surprising  feature  in  connection  with  the  severe  bark 
splitting  on  the  trunks  has  been,  in  many  cases,  the  comparatively 
slight  injury  to  the  tops  and  foliage.  Often  there  was  bark  splitting 
when  there  was  but  little  frost  damage  to  either  fruit  or  foliage. 

Some  lemon  groves  of  large  old  trees  were  observed  that  showed 
much  cracking  and  checking  on  the  limbs  and  trunks,  where  similar, 
adjoining  groves,  apparently  as  severely  injured,  showed  almost  no 
checking. 

While  it  is  true  that  in  most  cases  where  the  bark  was  split  and 
loosened  from  the  tree  it  was  killed,  it  does  not  follow  that  when 
the  bark  was  killed  it  always  loosened.  Instances  were  common  where 
trees  were  girdled  with  frozen  bark  and  the  bark  remained  perfectly 
tight.  Sometimes  these  girdled  trees  showed  no  foliage  damage  and 
there  would  be  no  suspicion  that  they  had  been  injured  until  sud- 
denly, perhaps  four  months  after  the  freeze,  the  leaves  would  droop 
and  the  tree  would  die. 

In  Florida  the  area  of  bark  immediately  around  the  bud-union 
is  very  susceptible  to  injury  by  freezing,  being  more  tender  than 
the  bark  on  other  portions  of  the  trunk.  This  greater  tenderness  of 
the  bud-union  was  not  noticeable  in  California,  the  bark  on  the  other 
portions  of  the  trunk  being  injured  just  as  readily  as  around  the 
bud-union.  In  California  the  point  most  susceptible  to  injury  seems 
to  be  in  the  crotches  of  the  limbs. 

BELATIVE  HARDINESS  OF  DIFFEEENT  VARIETIES  AND  SPECIES  OF 

CITRUS  FRUITS 

Relative  Hardiness  of  Trees. — The  freeze  brought  out  marked 
differences  in  the  hardiness  of  the  several  varieties  of  citrus  trees 
grown  in  California.  It  also  demonstrated  that  the  relative  hardiness 
of  the  trees  of  a  variety  is  not  the  same  as  the  relative  hardiness  of 
the  fruits  of  that  variety,  and  this  fact  must  be  borne  in  mind  in  order 
to  avoid  confusion. 


262  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

Orange  trees,  of  course,  proved  themselves  much  hardier  than 
lemon  trees.  It  was  common  to  see  lemon  trees  entirely  defoliated,  and 
among  them  orange  trees  which  had  lost  few  or  none  of  their  leaves. 
There  were  other  places  where  the  lemon  trees  were  partly  defoliated 
and  had  split  bark  in  the  limbs,  while  the  orange  trees  showed  no 
damage  except  in  the  fruit,  and  even  here  the  damage  was  so  limited 
that  the  grower  received  good  returns  for  his  crop. 

In  most  places  there  seemed  little  difference  in  hardiness  between 
Washington  navel  trees  and  Valencias,  this  being  especially  true  of  the 
bearing  trees. 

In  one  locality,  where  there  was  not  much  damage  to  the  bearing 
orange  trees,  a  careful  comparison  was  made  between  the  condition 
of  250  young  Valencias  and  the  same  number  of  navels.  These  trees 
were  all  of  the  same  age,  two  years  and  a  half  old  at  the  time  of  the 
freeze,  and  offered  an  opportunity  for  a  perfectly  fair  comparison. 
Fourteen  per  cent  of  the  navels  and  3  per  cent  of  the  Valencias  had 
the  limbs  killed;  64  per  cent  of  the  navels  and  93  per  cent  of  the 
Valencias  were  largely  defoliated  without  having  the  limbs  killed; 
22  per  cent  of  the  navels  and  4  per  cent  of  the  Valencias  were  only 
partially  defoliated.  In  this  case  the  navels  were  not  less  hardy  than 
the  Valencias,  but  the  amount  of  variation  was  greater  in  the  navels. 
More  navels  than  Valencias  were  badly  frozen,  but  there  were  also 
more  navels  than  Valencias  among  the  trees  which  were  only  slightly 
injured. 

The  conflicting  degrees  of  injury  exhibited  by  these  varieties  in 
different  places  indicate  that  they  are  naturally  of  about  the  same 
degree  of  hardiness  and  that  the  differences  observed  in  different 
places  were  due  to  the  varying  condition  of  the  trees  at  the  time  of 
the  freeze. 

There  was  a  marked  difference  in  the  hardiness  of  the  two  principal 
varieties  of  lemons,  the  Lisbons  showing  themselves  decidedly  more 
resistant  than  the  Eurekas.  Temperatures  low  enough  to  cause  Eureka 
trees  to  drop  three-fourths  of  their  leaves  were  withstood  by  Lisbons 
with  practically  no  foliage  damage  and  with  some  uninjured  fruit. 
Villafranca  lemons  proved  somewhat  hardier  than  Eurekas,  but  not 
so  hardy  as  Lisbons.  In  one  nursery  two-year-old  Eureka  and  Villa- 
franca trees  on  sweet  stock  were  found  side  by  side.  The  former  trees 
were  frozen  nearly  to  the  buds,  whereas  only  the  upper  half  of  the 
Villafranca  tops  were  killed. 

The  grapefruit  trees  proved  more  hardy  than  lemon  trees.  The 
fruit  of  the  pomelo  is  never  so  easily  frozen  as  the  orange  fruit,  but 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  263 

the  trees  usually  showed  themselves  somewhat  more  tender  than 
orange  trees. 

Among  the  other  varieties  of  citrus  trees  the  tangerines  and  the 
Satsuma  oranges  were  more  hardy  than  the  navels  and  Valencias. 
The  tangerine  tree  is  very  resistant,  and  many  cases  were  found 
where  this  tree  retained  its  foliage  alongside  of  orange  trees  that  had 
been  entirely  defoliated.  Only  two  groves  were  found  containing  King 
orange  trees,  and  in  both  of  these  instances  they  were  more  seriously 
injured  than  near-by  navel  orange  trees. 

Lime  trees  were  more  tender  than  lemons,  the  Tahite  lime  being 
more  hardy  than  the  Mexican.  The  citron  was  slightly  more  tender 
than  the  lime.  Several  instances  were  observed  where  lime  and  citron 
trees  were  growing  in  lemon  orchards;  and  in  such  cases  they  were 
entirely  defoliated  and  a  portion  of  the  brush  or  tops  killed  alongside 
of  lemon  trees  that  merely  lost  the  outer  layer  of  foliage. 

When  one  considers  that  the  citrus  tree  is  a  native  of  the  tropics,  it 
is  surprising  to  find  it  capable  of  standing  the  temperatures  of  the 
1913  freeze.  In  one  place  young  navel  orange  trees,  that  were  sub- 
jected to  a  minimum  temperature  of  5°  F.  above  zero,  came  through 
with  trunks  alive,  notwithstanding  that  the  navel  orange  was  brought 
to  the  United  States  from  a  place  only  12  degrees  south  of  the  equator. 

Relative  Hardiness  of  Fruit. — The  fruit  of  the  pomelo  was  less 
injured  by  the  cold  than  any  other  of  the  citrus  fruits.  Even  when 
the  skin  was  spotted  as  a  result  of  the  freezing  the  inside  pulp  often 
showed  no  breaking  and  remained  juicy.  In  this  respect  the  pomelo 
was  quite  different  from  the  orange,  because  there  was  always  a  notice- 
able injury  to  the  pulp  of  oranges  which  had  spotted  skin. 

The  comparative  injury  of  navel  and  Valencia  fruits  varied  with 
the  locality.  In  many  sections  there  seemed  to  be  little  difference  in 
the  condition  of  the  two  kinds  of  fruit,  but  where  there  was  a  differ- 
ence, it  was  more  common  to  find  the  injury  greater  in  the  Valencias. 
As  the  Valencia  is  the  later  variety,  the  fruit  was  less  mature  at  the 
time  of  the  freeze  than  were  the  fruits  of  the  navels.  In  Whittier,  and 
in  the  Sespe  Canon  in  Ventura  County,  the  Valencia  proved  to  be  more 
hardy  than  the  Washington  navel.  The  Thompson  Improved  navel 
proved  more  tender  than  the  Washington  navel  or  the  Valencia. 
Blood  oranges  ranged  about  the  same  as  Washington  navels. 

Although  the  tangerine  trees  are  so  hardy,  their  fruit  is  more 
easily  frozen  than  the  fruits  of  the  navel  and  Valencia. 

Lemon  fruit  is  injured  at  a  temperature  several  degrees  higher 
than  that  which  injures  oranges,  and  of  course  the  young,  small-sized 
lemons  are  more  tender  than  those  which  are  large  enough  to  be  picked. 


264  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

It  has  been  supposed  that  lemons  can  withstand  a  temperature  of 
28°  F.  without  injury,  but  whether  the  crop  of  small  fruit  can  be 
exposed  to  this  temperature  without  loss  has  never  been  determined 
with  sufficient  accuracy  to  be  convincing.  The  tendency  among  the 
best  orchardists  is  to  regard  any  temperature  below  32°  F.  as 
dangerous.* 

Lisbon  fruit  was  less  easily  damaged  than  that  of  Eurekas.  The 
difference  did  not  seem  to  be  due  entirely,  at  any  rate,  to  the  heavier 
foliage  of  the  Lisbons,  because  the  fruit  of  the  heavy  foliage  type  of 
Eureka  was  injured  more  than  the  Lisbon  fruit. 

Yellow  or  tree-ripe  lemons  were  more  sensitive  to  frost  injury  than 
either  the  large-sized  silver  or  green  fruit.  The  packing-house  reports 
from  one  young  grove  showed  practically  no  loss  of  the  large-sized 
green  fruit,  and  only  15  per  cent  frozen  fruit  in  the  silver ;  while  the 
tree-ripes  were  a  total  loss.  This  comparative  resistance  between  the 
yellow  or  tree-ripe  and  the  green  fruit  was  found  to  be  quite  general. 


NATUEAL  FACTOES  INFLUENCING  THE  TEMPEEATUEE 

Elevation. — Comparative  elevation  is  a  very  important  element  in 
influencing  temperature.  It  was  common  to  hear  people  remark,  soon 
after  the  freeze,  that  it  was  colder  this  year  on  the  higher  levels  than 
it  was  on  the  lower  ground;  but  this  was  not  generally  so.  Investi- 
gation showed  that  as  usual  the  lower  portions  of  most  districts  were 
colder  than  the  higher  land  of  those  districts.  There  were  many 
places  where  this  advantage  of  the  higher  ground  was  clearly  illus- 
trated in  a  single  grove.  In  such  groves  a  gradual  transition  could 
be  seen  from  the  uninjured  fruit  and  foliage  of  the  higher  portions 
to  entirely  defoliated  trees  below. 

It  must  be  understood  that  it  is,  in  all  cases,  the  relative  elevation 
that  is  important,  not  the  actual  elevation  above  sea-level.  An  ad- 
joining low  area,  valley,  or  arroyo  that  afforded  opportunity  for  the 
cold  air  to  drain  off  was  in  this  freeze,  as  in  other  freezes,  of  decided 
advantage. 

There  were  some  places,  nevertheless,  where,  contrary  to  the  rela- 
tions existing  in  most  years,  the  damage  on  the  higher  ground  was 
greater  than  farther  down  the  slope.  In  Upland  this  was  shown  by 
the  condition  of  the  street  trees,  the  pepper  trees  at  the  top  of  the  hill 
being  defoliated  and  those  lower  down  showing  only  slight  damage. 

*  Compare  article  on  ' '  Eeeent  Investigations  in  Orchard  Heating, "  by  I.  G. 
McBeth  and  J.  E.  Allison,  The  California  Citrograph,  January,  1919,  p.  51. 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  265 

Protective  Hills. — The  damage  done  by  freezing  was  closely  cor- 
related with  the  injury  done  to  the  trees  by  the  severe  wind. 

It  was  probably  on  this  account  that  plantings  which  were  shel- 
tered on  the  north  by  hills  passed  through  the  cold  wave  in  much 
better  condition  than  areas  that  received  the  unintercepted  blast 
from  the  north.  It  looked  in  many  cases  as  if  the  hills  were  so  located 
that  a  body  .of  warm  air  had  been  locked  in  around  the  trees,  and  that 
the  cold  north  wind  had  slipped  over  these  pocketed  areas. 

Again,  the  presence  of  a  mountain  range  along  the  south  side  of 
certain  sections  apparently  accounts  for  the  little  injury  to  fruit, 
probably  due  to  a  more  gradual  thawing  of  the  fruit  so  situated.  In 
still  other  sections  there  appeared  to  be  no  frost  high-line,  and  the 
higher  orchards,  located  along  a  north  slope,  appeared  to  be  as  severely 
injured  as  the  lower  orchards. 

Influence  of  Canons. — In  previous  years  the  territory  about  the 
mouths  of  canons  has  usually  been  favored  during  cold  weather.  The 
current  of  air  coming  down  the  canon  has  kept  the  air  well  mixed 
and  prevented  the  stratification  which  takes  place  when  the  air  stag- 
nates. This  year  it  seems  that  the  whole  mass  of  air,  which  moved 
down  over  the  mountains,  was  below  the  freezing  temperature,  and 
cold  air  in  motion  is  much  more  damaging  than  quiet  air  of  the  same 
temperature,  so  that  many  of  the  canons  this  year  changed  their 
nature.  This  was  not  universally  true,  for  there  were  some  canons 
which  gave  no  evidence  of  being  sources  of  streams  of  cold  air.  The 
groves  nearest  to  the  San  Gabriel  Canon,  for  instance,  were  not  dam- 
aged so  much  as  groves  farther  out  in  the  valley.  The  San  Antonio 
Canon,  on  the  other  hand,  was  very  cold,  judging  by  the  appearance 
of  the  groves  near  its  mouth.  The  San  Antonio  Canon  takes  the  same 
general  north  and  south  direction  as  that  of  the  wind  which  ushered 
in  the  cold,  while  the  San  Gabriel  Canon  runs  northeast  and  southwest 
in  its  lower  portion  and  nearly  east  and  west  in  its  upper  forks. 

Water  Protection. — The  protection  afforded  by  nearness  to  bodies 
of  water  of  considerable  size,  which  was  shown  to  be  of  very  great 
importance  in  Florida,  where  there  are  many  lakes  and  inland  bays, 
was  of  very  little  importance  in  California.  In  a  general  way  the 
less  injury  to  trees  near  the  coast  may  in  a  measure  be  due  to  the 
modifying  influence  on  the  cold,  exercised  by  the  nearness  of  the  ocean. 
Doubtless  nearness  to  the  ocean  failed  to  give  any  very  marked 
indication  of  water  protection,  primarily  because  the  wind  accom- 
panying the  freeze  was  from  the  landward  side. 

Protection  Afforded  Fruit  by  Location  on  Tree. — The  location  of 
fruit  on  the  tree  frequently  exercised  an  influence  on  the  damage 


266  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

produced.  When  fruit  happened  to  rest  upon  the  ground  it  usually 
remained  uninjured,  even  when  all  of  the  rest  of  the  fruit  of  the  tree 
was  frozen  so  that  it  soon  became  juiceless.  Because  fruit  which 
touched  the  ground  was  so  protected  it  does  not  follow  that  fruit 
which  was  near  the  ground  was  less  damaged  than  fruit  higher  in  the 
tree.  The  reverse  was  usually  the  case. 

While  there  was  no  advantage  to  the  fruit  in  being  near,  the  ground, 
it  did  receive  some  protection  when  tucked  in  among  the  leaves  of 
the  tree.  One  of  the  most  promising  sections  of  an  orange  tree  on 
which  to  find  fruit  good  to  eat  was  in  the  foliage  on  the  south  side  of 
the  tree.  Fruit  in  this  position  on  the  tree  very  likely  passed  through 
more  gradual  changes  in  temperature  both  in  freezing  and  in  thawing 
than  fruit  in  more  open  situations. 


ARTIFICIAL  METHODS  OF  PEOTECTING  GEOVES 

Along  with  the  natural  modifying  agents  of  the  temperature,  such 
as  elevation,  hills,  and  canons,  there  were  a  number  of  artificial  causes 
which  modified  the  cold.  The  most  important  of  these  was  the  heating 
which  was  done  in  so  many  groves.  Windbreaks,  running  water, 
wrapping  of  the  trees,  and  lath  covering  are  things  which  must  also 
be  considered. 

Windbreaks. — The  question  of  windbreaks,  their  benefit,  and  det- 
riment, and  the  comparative  value  of  different  trees  for  such  purposes, 
has  been  for  many  years  a  constant  source  of  discussion.  The  ideal 
windbreak  seems  to  be  the  Monterey  cypress  and  the  blue-gum  planted 
alternately  in  one  row,  the  trees  set  five  to  six  feet  apart.  In  such 
windbreaks  the  cypress  forms  a  tight  base  and  the  Eucalyptus  gives 
the  desired  height. 

The  tendency  during  the  past  few  years  in  many  sections  has  been 
to  remove  windbreaks,  for  they  have  served  in  some  places  to  prevent 
air  drainage,  and  increase  the  damage  from  frosts,  where  their  need 
as  wind  shields  was  not  important.  There  are  other  sections  which 
are  annually  visited  by  strong  winds  where  they  are  rightly  regarded 
as  indispensable. 

In  most  groves  the  three  or  four  rows  on  the  leeward  side  of  the 
windbreak  were  less  injured  by  the  freeze  than  those  in  other  parts 
of  the  orchard,  but  it  was  rare  to  find  any  frost  protection  more  than 
five  rows  away  from  the  hedge.  It  is  not  clear  that  all  of  this  pro- 
tection was  due  to  the  modifying  of  the  temperature  by  the  wind- 
break, as  the  orchard  rows  next  to  the  windbreak  are  frequently  much 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  267 

drier  than  the  other  trees  of  the  grove,  as  is  made  evident  by  the 
lighter  crops  on  these  rows,  and  this  puts  these  trees  in  a  different 
condition  to  resist  cold.  It  has  been  found  that  trees  that  were  dry, 
provided  they  were  not  actually  suffering  and  weakened  because  of 
drought,  were  less  easily  damaged  by  the  cold  than  trees  which  had 
a  more  plentiful  supply  of  sap  or  were  in  more  active  growth. 

A  few  groves  were  found  where  the  rows  next  to  the  windbreak 
had  been  kept  in  practically  as  good  condition  as  the  other  trees  of 
the  grove  by  giving  them  extra  water  and  fertilizer.  In  some  of  these 
groves  it  was  also  possible  this  year  to  notice  a  slightly  better  condition 
of  the  rows  next  to  the  windbreak. 

It  seems  certain  from  all  of  the  evidence  collected  that  windbreaks 
did  exercise  a  distinctly  modifying  effect  in  this  freeze  on  the  damage 
caused  to  the  trees  for  a  short  distance  to  the  leeward  of  them;  but 
this  advantage  was  slight,  and,  in  view  of  the  rareness  of  the  occur- 
rence of  such  severe  freezes  accompanied  by  wind,  it  would  not,  as  a 
whole,  seem  wise  to  advocate  the  use  of  windbreaks  for  frost  pro- 
tection only.  They  take  up  much  valuable  space  and  when  the  tem- 
perature is  that  of  a  "frost"  rather  than  a  freeze  the  protection  that 
the  windbreak  gives  to  the  leeward  side  is  likely  to  be  offset  by  the 
increase  in  damage  on  the  windward  side. 

Effect  of  Running  Water  or  Irrigation  During  Freeze. — One  of  the 
first  methods  of  protection  to  suggest  itself  to  growers  was  to  run 
water  through  the  grove.  The  water  would  have  to  give  up  much 
heat  in  being  cooled,  and  if  water  freezes  a  large  amount  of  heat  is 
released. 

When  conditions  were  such  that  all  the  factors  were  the  same 
except  for  the  presence  of  running  water,  the  groves  that  were  under 
water  sometimes  looked  better  than  those  which  were  not. 

In  one  grove  only  5  per  cent  of  the  fruit  (navels)  from  that  portion 
of  the  orchard  which  was  irrigated  during  the  cold  was  rejected  at 
time  of  shipping,  whereas  100  per  cent  of  the  fruit  from  the  non- 
irrigated  portion  was  frozen.  Other  conditions  were  apparently  sim- 
ilar. The  fruit  was  picked  some  time  previous  to  March  28. 

In  three  citrus  nurseries  well  defined  benefit  from  running  water 
during  the  freeze  was  apparent,  and  one  small  orchard  of  500  one- 
year-old  Valencia  trees  was  found  where  one-half  of  the  trees  had 
been  irrigated  during  the  entire  cold  spell  from  Sunday  afternoon 
until  Wednesday  morning.  Ten  per  cent  of  the  non-irrigated  trees 
were  killed  and  the  outer  layer  of  growth  on  the  remaining  90  per 
cent  was  badly  injured,  while  the  irrigated  trees  showed  practically 
no  frost  injury. 


268  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

While  the  above  instances  would  indicate  that  considerable  pro- 
tection might  be  obtained  from  running  water  through  a  grove  during 
a  freeze,  it  should  be  stated  that,  in  very  many  instances,  little  dif- 
ference could  be  seen  between  the  groves  that  were  under  water  and 
those  that  were  dry,  and  in  but  few  cases  did  the  trees  under  water 
show  any  greater  vigor  in  putting  out  new  growth. 

In  general  it  seems  that  one  should  not  rely  upon  the  use  of  run- 
ning water  to  protect  the  fruit  from  freezing.  In  case  of  emergency 
no  harm  will  come  from  running  it,  and  if  the  temperature  does  not 
go  too  low  a  slight  benefit  may  result. 

Effect  of  Spraying  Water  on  Trees. — In  a  few  places,  and  on  a 
few  trees  only,  water  was  sprayed  upon  trees  in  order  to  keep  them 
from  freezing.  This  soon  gave  the  trees  a  heavy  coating  of  ice,  and 
spraying  was  stopped  so  that  the  ice  would  not  become  thick  enough 
to  break  the  limbs.  In  the  few  cases  which  were  found  where  this 
spraying  had  been  done  the  practice  seemed  to  have  little  value. 

In  the  case  of  seed-beds  or  small  nursery  stock  that  would  not  be 
injured  by  a  heavy  coating  of  ice  this  method  of  protection  might  be 
very  effective.  In  a  freeze,  such  as  that  under  consideration  in 
California,  it  may  be  questioned  whether  the  injury  that  would  be 
caused  by  such  a  protective  treatment  would  not  in  general  be  as 
great  as  the  damage  resulting  from  the  frost  injury.  Again,  it  will 
never  be  possible  for  all  groves  to  have  a  sufficient  supply  of  water 
for  such  protection  at  the  same  time,  unless  a  reserve  water  supply 
is  retained  in  special  reservoirs  for  each  grove. 

Effect  of  wrapping  Trees. — The  difficulty  of  artificially  heating  a 
young  grove  is  greater  than  with  older  groves,  where  the  trees  are 
larger  and  the  hot  air  is  more  easily  retained.  The  results  obtained 
by  .wrapping  the  trunks  of  young  trees  are  therefore  of  much  practical 
importance,  for  if  there  are  ways  of  protecting  young  trees  which  are 
cheaper  than  heating  the  best  of  these  ways  should  be  known. 

The  principal  substances  used  during  the  freeze  for  trunk  wrap- 
pers were  cornstalks,  tule,  newspapers,  and  tar  paper.  Many  young 
trees  had  protectors  about  their  trunks  made  of  yucca,  tar  paper,  or 
perforated  paraffined  paper.  These  protectors  are  rectangular  pieces, 
which  had  been  bent  around  the  trunks,  forming  hollow  cylinders, 
there  being  an  air  space  between  the  trunk  and  the  protector.  They 
had  been  put  around  the  trees  during  the  summer  to  prevent  the 
sunburning  of  the  bark  or  its  mechanical  injury,  and  were  not  gener- 
ally regarded  as  frost  protectors. 

Cornstalks  afforded  a  good  measure  of  protection  when  enough  of 
them  were  used,  and  when  they  were  bound  firmly  enough  to  keep 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  269 

them  in  place  and  to  press  them  together,  so  that  the  free  movement 
of  the  air  between  them  was  prevented.  In  some  cases  earth  was 
thrown  up  around  the  base  of  the  trees,  so  as  to  cover  the  lower  ends 
of  the  stalks  a  foot  or  so  deep.  There  were  young  groves  of  two-year- 
old  trees  wrapped  in  this  way  that  received  little  injury  except  to 
the  exposed  foliage  of  the  last  season's  growth,  while  near-by  groves 
which  were  carelessly  wrapped  or  which  were  left  unwrapped  were 
badly  frozen. 

One  of  the  most  marked  cases  of  benefit  from  paper  wraps  was 
observed  in  a  four-year-old  lemon  grove,  the  trunks  of  which  had  been 
scored  during  the  summer  preceding  the  freeze.  All  the  trunks  in 
the  lower  half  of  this  orchard  were  well  wrapped  with  paper,  but  in 
the  upper  half  (the  grove  being  on  a  gentle  slope  with  south  exposure) 
no  frost  injury  was  expected,  and  this  precaution  of  wrapping  was 
not  taken.  In  the  latter  case  severe  bark-splitting  occurred,  it  being 
necessary  to  renew  some  trees  from  sprouts;  but  in  the  lower  and 
colder  portion  of  the  property  there  was  no  such  injury  beneath  the 
paper  wraps.  The  degree  of  frost  injury  to  the  foliage  and  tops, 
however,  was  in  indirect  proportion  to  the  elevation.  It  is  very 
essential  in  wrapping  the  trunks  to  get  the  wrap  well  down  to  the 
ground,  and  there  is  no  reason  why  the  entire  trunk,  instead  of  only 
the  lower  half  or  three-quarters,  cannot  be  protected  if  wraps  of 
sufficient  length  are  obtained. 

The  protectors  made  of  yucca,  paraffined  paper,  tar  paper,  and  the 
like,  open  at  the  top,  furnished  some  protection,  but  are  not  equal  to 
good  newspaper  or  cornstalk  wrapping.  The  only  serious  objection 
which  has  been  raised  to  the  use  of  protectors  is  that,  under  certain 
conditions,  they  favor  the  development  of  gum  disease. 

When  young  trees  are  tightly  wrapped  as  a  protection  against 
frost,  it  is  important  to  remove  the  wrapping  before  hot  weather,  as 
otherwise  serious  injury  may  result. 

Protection  ~by  Lath-houses,  Burlap,  or  Cloth  Coverings. — Lath- 
houses,  burlap,  or  canvas  coverings  afforded  good  protection  to 
seed-bed  stock  up  to  a  few  degrees  of  frost. 

Lath-houses  kept  the  temperatures  within  them  warmer  than  the 
temperatures  outside.  In  one  instance  the  temperature  near  the 
middle  of  a  large  lath-house  was  4  degrees  higher  than  the  outside 
temperature.  It  was  found  in  this  case  that  it  was  a  degree  or  so 
warmer  at  the  center  of  the  house  than  nearer  the  sides.  Even  where 
there  was  a  covering  of  lath  without  any  sides,  the  plants  beneath  the 
lath  were  affected  much  less  than  those  without  any  covering.  Part 
of  the  protection  of  the  lath-house  is  due,  doubtless,  to  the  shading 

DIVISION  OF  SUbtKOPICAL  HORTICULTURE 
COLLEGE  OF  AGRICULTURE 

FV     PAI  IPORNIA 


270  UNIVERSITY  OP  CALIFORNIA EXPERIMENT  STATION 

which  it  furnishes,  causing  a  more  gradual  warming  of  the  plants 
after  the  frost.  At  night  the  lath  probably  reflects  back  some  of  the 
heat  radiated  from  the  ground,  and  it  also  shuts  in  a  pocket  of  warm 
air. 

PKOTECTION  BY  AETIFICIAL  HEATING 

The  cold  weather  of  January,  1913,  demonstrated  to  the  citrus 
growers  of  Southern  California  that  the  only  successful  way  thus 
far  devised  for  fighting  cold  weather  is  the  use  of  orchard  heaters. 
To  be  sure,  success  was  not  universal  with  those  who  tried  to  heat 
their  groves,  but  there  were  enough  successes  to  show  that  where  the 
equipment  and  supplies  are  adequate  and  the  work  well  done  orchard 
heating  is  effective. 

So  much  doubt  has  existed  in  the  minds  of  many  growers  as  to 
whether  artificial  heating  is  effective  and  pays  that  special  observations 
on  selected  plots  of  heated  and  unheated  areas  were  made  by  several 
investigators.  A  report  on  some  of  these  observations  will  be  given 
as  a  separate  article  in  another  part  of  this  bulletin.  General  state- 
ments only  will  be  given  here. 

Acreage  and  General  Results. — In  all  there  were  several  thousand 
acres  in  California  that  had  been  equipped  with  orchard  heaters  for 
the  winter  of  1912-13.  In  a  part  of  this  acreage  the  equipment  was 
entirely  inadequate  and  allowed  only  a  weak  and  ineffective  effort  to 
be  made  when  the  cold  weather  came.  In  general,  however,  those 
who  tried  to  heat  their  groves  obtained  results  which  satisfied  them 
that  it  had  paid.  There  were  many  heated  groves  where  the  entire 
crop  was  saved  and  where  the  trees  showed  no  effects  of  the  cold, 
while  neighboring  groves  which  were  unheated  lost  their  crop  of  fruit 
and  suffered  such  tree  damage  that  it  was  two  years  or  more  before 
they  began  to  pay  expenses.  In  some  lemon  groves  where  successful 
heating  was  done  the  fruit  from  the  first  pick,  which  was  made  after 
the  freeze,  brought  enough  to  pay  the  entire  cost  of  heating,  including 
the  cost  of  the  equipment,  and  then  paid  the  grower  a  good  profit 
besides.  In  addition  to  saving  the  fruit  which  brought  in  these  returns, 
the  young  fruit  and  bloom  of  these  trees  was  not  frozen  and  there 
was  no  injury  to  the  fruiting  wood.  Results  were  not  always  so 
satisfactory  as  this,  but  failure  could  always  be  traced  to  improper 
equipment,  a  shortage  of  fuel,  or  a  lack  of  vigilance.  Failures  were 
seldom  complete,  however,  and  the  condition  of  the  trees  usually 
showed  benefit  from  the  heating,  even  when  the  crop  was  lost. 

Equipment  and  Material. — Most  of  the  heating  was  done  with  pots 
burning  oil,  many  kinds  of  which  were  in  use  in  different  groves.  In 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA 


271 


Fig.  7. — On  left  an  orchard  coal  heater.  This  is  merely  an  open  firebox 
with  grate  at  bottom.  In  center,  the  simplest  type  of  orchard  oil  heater, 
being  merely  an  open  pail-like  structure  with  holes  at  top  for  air  draft, 
on  right,  a  type  of  torch  used  in  lighting  heaters,  supplied  with  asbestos  wick 
and  burning  distillate  or  kerosene.  Photo  by  Barrett. 


Fig.  8. — On  right  one  of  the  typos  of  orchard  oil  heaters  very  commonly 
used  at  the  time  of  the  1913  freeze,  having  a  sliding  top  and  with  openings 
on  the  side  for  air  draft.  On  left  one  of  the  best  orchard  heaters  that  has 
been  perfected  since  1913.  The  smoke  stack  and  drafts  are  hidden  by  the 
cover  which  is  lifted  off  when  heater  is  lighted.  Photo  by  Barrett. 


272  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

a  few  groves  baskets  and  stoves  burning  coal  were  used,  but  in  general 
these  did  not  give  as  satisfactory  results  as  the  oil  heaters  (fig.  7). 
Oiled  shavings  burned  in  the  grove  gave  little  help,  and  is  a  method 
that  cannot  be  depended  upon. 

The  oil  pots  used  varied  in  capacity  from  one  to  four  gallons. 
Some  of  them  were  open  pots,  the  shape  of  flower-pots,  some  were 
rectangular  with  sliding  tops,  and  others  were  either  oblong  or  round 
and  provided  with  stacks  (fig.  8).  The  pots  which  had  stacks  had 
the  tops  covered,  but  had  drafts  which  could  be  opened  to  let  in  the  air. 
The  oil  used  was  a  low  grade  crude  oil  with  asphaltum  base,  and  cost, 
when  put  down  in  the  grove,  about  3  cents  a  gallon. 

The  lighting  was  commonly  done  by  means  of  torches  that  held  a 
gallon  of  fuel,  and  had  a  long  spout,  inclosing  an  asbestos  wick. 
Engine  distillate,  gasoline,  or  kerosene  was  used  as  fuel,  and  when  the 
torch  was  tipped  some  of  the  burning  liquid  fell  into  the  pot  (fig.  7). 

In  some  cases  where  new  heaters  were  being  used  considerable  delay 
was  occasioned  by  the  difficulty  in  lighting  the  pots,  several  visits 
with  the  torch  being  necessary.  After  pots  had  been  burned  for 
some  time  and  had  become  thoroughly  sooted  the  lighting  was  accom- 
plished fairly  easily.  In  order  to  avoid  such  interruption  at  a  critical 
period,  it  seems  desirable,  either  to  place  a  bundle  of  excelsior  in  the 
chimney  of  each  heater,  or  to  light  and  burn  each  heater  for  a  half- 
hour  or  more  before  they  are  required  to  be  lighted  during  a  freeze 
(fig.  9). 

The  pots  were  filled  from  tank-wagons.  Sometimes  the  oil  was 
drawn  from  the  tank-wagon  into  buckets  and  poured  into  the  pots 
and  sometimes  a  hose  was  attached  to  the  tank  and  the  oil  run  directly 
into  the  pots.  The  tank-wagons  were  filled  from  storage  tanks  which 
were  made  of  steel  or  of  concrete. 

These  varied  in  capacity  according  to  the  acreage  and  estimated 
needs,  and  many  growers  found  that  their  estimates  had  been  too  low. 
When  twenty  or  twenty-five  cold  nights  may  be  expected  it  is  well  to 
have  a  storage  capacity  of  about  1000  to  1500  gallons  per  acre  in 
addition  to  full  pots. 

As  a  result  of  the  difficulties  experienced  in  this  freeze  the  tendency 
hereafter  will  be  to  use  larger  pots  of  seven  to  ten  gallons  capacity  and 
thus  avoid  the  necessity  of  refilling  in  the  night.  The  night  filling 
is  expensive,  because  of  the  higher  wage  paid  the  men  and  the  smaller 
amount  of  work  which  they  do  in  the  night  than  in  the  day,  and  is 
responsible  for  much  of  the  spilling  of  oil  which  occurs  during  the 
filling  of  the  pots.  The  oil  kills  the  roots  with  which  it  comes  in 
contact,  besides  rendering  the  soil  unfit  for  use.  Some  growers  spent 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA 


273 


as  high  as  50  cents  a  tree  in  removing  this  oiled  soil  from  their  groves 
after  the  freeze. 

One  conclusion  very  definitely  reached  by  growers,  largely  from 
the  results  obtained  in  this  freeze,  is  that  in  the  heating  of  an  orchard 
it  is  stoves  radiating  actual  heat  that  is  needed,  and  not  those  pro- 
ducing a  smudge.  The  smoke  given  off  by  the  oil  heaters  collects  to 
some  extent  on  the  fruit  and  is  difficult  to  remove. 


Fig.  9. — Lighting  a  good  recent  type  of  orchard  heater  by  means  of  a 
torch  containing  distillate.  The  fire  being  applied  to  a  small  amount  of 
excelsior  placed  in  the  tube  of  the  down  draft.  The  cover  on  the  right  when 
placed  on  the  heater,  extinguishes  the  fire  and  excludes  rain.  Photo  by 
Barrett. 

Methods. — The  groves  in  which  the  best  work  was  done  Avere 
equipped  with  one  pot  to  the  tree.  These  burned  approximately  100 
gallons  an  hour  per  acre,  when  they  were  all  going  full  blast.  At 
these  times  the  temperature  of  the  grove  was  often  from  8  to  12 
degrees  higher  than  the  temperatures  in  neighboring  unheated  groves. 
Of  course  it  was  only  during  the  coldest  weather  that  it  was  necessary 
to  have  all  the  pots  burning  at  full  capacity.  Usually  only  one-fourth 
or  one-half  of  the  pots  were  lighted,  and  after  these  had  burned  a 
time  they  were  extinguished  and  another  portion  lighted,  so  that 


274  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

enough  oil  was  retained  in  the  former  to  allow  for  relighting  them  in 
case  of  a  sudden  drop  in  temperature. 

It  was  found  difficult  by  many  growers  to  get  the  right  kind  of 
labor  and  to  get  the  help  when  needed.  The  use  of  larger  pots  will 
reduce  the  amount  of  night  labor  needed,  and  the  small  ranch  of  ten 
acres  ought  to  be  handled  successfully  by  two  men,  if  they  are  vigilant 
and  if  their  methods  are  correct. 

Temperature  at  Which  to  Fire. — The  experiences  of  the  past  have 
shown  that  one  of  the  most  necessary  precautions  to  take  is  to  begin 
heating  soon  enough.  There  is  general  agreement  that  it  is  easier  to 
hold  a  temperature  than  to  raise  it  after  it  has  gone  too  low.  For 
this  reason  some  of  those  who  have  had  most  experience  in  heating 
are  planning  to  begin  lighting  for  lemons  at  31  degrees.  With  oranges 
a  degree  or  two  lower  than  this  may  be  risked  before  beginning 
operations.* 

It  has  also  proved  of  advantage  to  bank  extra  pots  outside  of  the 
grove  along  the  windward  side.  Not  only  is  this  necessary  in  order 
to  protect  the  outside  rows  but  it  makes  it  much  easier  to  hold  the 
temperature  within  the  orchard. 

Value  of  Combined  Effort. — Where  large  blocks  of  groves  were 
heated  the  task  of  heating  was  easier  than  when  the  heated  areas  were 
small  and  isolated.  The  effects  from  the  heating  on  a  large  acreage 
were  often  noticeable  at  a  considerable  distance  from  the  groves  where 
the  firing  was  being  done.  In  one  section  the  heating  of  one  hundred 
acres  produced  a  rise  in  temperature  of  from  2  to  3  degrees  in  groves 
a  mile  distant  as  soon  as  the  smoke  reached  these  groves.  The  co- 
operation of  growers  in  the  vicinity  of  Pomona  forms  a  notable  ex- 
ample of  the  benefit  of  such  combined  effort.  The  co-operation  can 
profitably  extend  to  the  employment  of  special  observers,  maintenance 
of  special  danger  calls,  employment  of  labor,  purchase  and  storage  of 
supplies,  and  the  like. 

Causes  of  Failure. — The  principal  causes  of  failure  in  the  heating 
done  in  1913  may  be  briefly  stated  as  follows : 

1.  The  use  of  pots  which  were  too  small.    These  burned  out  quickly 
and  were  difficult  to  refill. 

2.  Insufficient  number  of  pots  per  acre. 

3.  Shortage  of  fuel. 

4.  The  use  of  fuel  which  did  not  give  off  enough  heat. 

5.  Allowing  temperatures  to  go  too  low  before  lighting. 

*  See  article  by  J.  G.  McBeth  and  J.  E.  Allison,  California  Citroffraph,  Jan., 
1919,  p.  51. 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  275 

6.  Accumulation  in  the  pots  of  a  residue  of  asphaltum,  which 
burned  with  difficulty. 

7.  Growers  relying  upon  other  people's  reports  of  temperatures 
in  other  groves  rather  than  keeping  track  of  the  temperatures  in 
different  parts  of  their  own  groves. 

8.  Discouragement  after  partial  failure.     This  sometimes  proved 
disastrous. 

9.  Insufficient  amount  of  labor. 
10.  Incapable  labor. 

Costs  of  Heating. — The  exact  cost  of  firing  in  most  cases  has  been 
difficult  to  ascertain,  and,  although  considerable  data  has  been  gath- 
ered on  this  subject,  most  of  it  is  too  incomplete  to  make  it  of  value 
for  general  conditions.  From  the  data  given  in  connection  with  a 
twenty-five  acre  orchard  in  the  San  Fernando  Valley  we  find,  after 
figuring  6  per  cent  interest  on  the  total  equipment  and  20  per  cent 
depreciation  of  the  latter,  besides  cost  of  fuel  and  labor,  the  total  cost 
amounted  to  5.09  cents  per  gallon  of  oil  burned.  The  pots  were 
lighted  on  nine  different  nights.  A  similar  estimate  from  one  ranch 
in  Ventura  County,  which  had  one  hundred  acres  of  orchard  pro- 
tected with  heaters,  gives  5.78  cents  as  total  cost  per  gallon  of  oil 
burned.  In  this  case  the  pots  were  lighted  fourteen  different  nights. 
Near  Santa  Ana  the  heaters  on  an  eight-acre  orange  grove  were  lighted 
three  different  nights,  thus  saving  the  fruit  from  considerable  frost 
injury.  In  this  case  the  cost  amounted  to  6.13  cents  per  gallon  of 
oil  burned.  In  the  Pacific  Rural  Press,  May  24,  1913.  figures  given 
by  Mr.  T.  R.  Woodbridge  of  Upland  show  a  total  cost  of  6.5  cents  per 
gallon  of  oil  consumed. 

The  cost  of  the  heating  operations  have  varied  of  course  with  the 
amount  of  heating  which  was  done.  In  table  2  data  are  given  on 
the  cost  of  heating  in  twelve  groves  selected  from  different  parts  of 
Southern  California.  These  groves  were  more  or  less  successfully 
heated.  One  grower,  who  kept  a  very  accurate  account  of  all  of  his 
expenditures,  found  that  his  average  cost  of  heating  an  acre  for  one 
hour  was  $1.24.  His  grove  was  one-half  lemons  and  one-half  oranges, 
and  the  cost  of  heating  the  lemons  was  64  per  cent  of  the  entire  cost. 
The  fruit  was  saved  in  the  oranges  and  in  half  of  the  lemons,  but  in 
the  other  half  of  the  lemons  the  equipment  was  inadequate  and  the 
fruit  was  lost. 

In  the  tables  the  total  number  of  nights  fired  is  given.  On  some 
of  these  nights  the  heating  was  required  for  only  a  few  hours,  while 
at  other  times  it  was  needed  during  the  entire  night.  The  interest 
on  the  investment  has  been  figured  at  7  per  cent.  The  amount  charged 


276 


UNIVERSITY  OP  CALIFORNIA — EXPERIMENT  STATION 


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EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  277 

off  to  depreciation  has  varied  according  to  the  equipment  and  the 
usage  that  it  received.  The  depreciation  on  the  oil  heaters  has  usually 
been  as  high  as  25  per  cent  and  that  on  the  other  equipment  probably 
about  10  per  cent. 

The  cost  in  the  groves  where  the  best  work  was  done  ranged  from 
5l/2  to  6l/2  cents  per  gallon  of  oil  consumed;  or,  figured  on  the  acre 
basis,  from  $50  to  $100  an  acre  was  spent  in  these  groves.  With 
increased  experience  and  improved  equipment,  it  ought  to  be  possible 
in  the  future  to  lower  these  costs.  At  present  the  items  of  labor  and 
of  depreciation  contribute  too  large  a  percentage  to  the  total  cost. 
The  equipment  of  the  future  will  probably  last  longer  and  require 
less  attention  during  its  operation.* 

FACTORS   INFLUENCING   RESISTANCE    OF   TREES   TO   COLD   INJURY 

It  has  already  been  noted  that  there  was  a  marked  difference  in 
the  resistance  that  different  citrus  trees  showed  toward  the  cold 
weather.  Trees  side  by  side  were  often  very  differently  affected. 
It  was  evident  that  these  differences  were  not  always  due  to  differences 
in  temperature,  and  a  search  was  made  to  discover  why  certain  trees 
should  have  withstood  the  cold  so  much  better  than  others. 

Dormancy  of  Trees. — Trees  that  were  dormant  and  inactive  were 
able  to  stand  much  more  than  those  which  were  growing  and  where 
the  parts  of  the  plant  were  actively  functioning.  Orchardists  recog- 
nize this  fact  by  their  expression  that  trees  in  a  "sappy"  condition 
are  more  easily  damaged  than  trees  which  are  more  "mature." 

The  treatments  that  stimulate  a  tree  to  growth  or  to  activity,  there- 
fore, should  be  omitted,  if  possible,  when  cold  weather  is  to  be  expected. 
This  applies  particularly  to  young  trees.  Some  growers  feel  that  with 
lemons,  at  least,  it  is  more  profitable  to  keep  the  trees  growing  through 
the  cold  weather  and  protect  them  from  damage  by  heating. 

Some  of  the  things  which  influence  the  dormancy  of  citrus  trees, 
as  recorded  by  the  freeze,  are  dryness  and  the  time  of  irrigation, 
pruning,  and,  in  young  trees,  the  time  of  planting. 

Time  of  Planting. — Young  trees  which  were  planted  so  late  in  the 
fall  that  they  had  not  started  to  grow  at  the  time  of  the  freeze  were 
much  hardier  than  trees  similarly  located  that  had  been  planted  in 
the  summer  or  in  the  spring  and  were  growing.  In  one  young  grove, 
that  was  set  in  the  spring  of  1912,  most  of  the  growing  trees  were 

*  The  California  Cultivator,  Los  Angeles,  June  26,  1913,  gives  some  excellent 
articles  on  the  protection  of  citrus  groves  against  cold. 

The  Pacific  Rural  Press,  San  Francisco,  May  24,  1913,  has  an  excellent  state- 
ment on  cost  of  heating. 

The  Monthly  Bulletin,  State  Commission  of  Horticulture,  vol.  3,  no.  1,  has  an 
article  giving  costs  of  heating  a  large  acreage. 


:ITRICULTTJ:RE 


278  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

killed  half  way  to  the  ground,  while  trees  that  had  not  started  were 
uninjured.  In  another  grove  of  two-year-old  trees  some  resets,  that 
had  been  planted  in  the  fall,  mere  green  sticks,  were  uninjured,  while 
the  two-year-old  trees  all  about  them  were  killed  to  the  ground. 

Dryness. — It  was  very  common  to  find  trees  which  on  account  of 
being  dry  were  less  injured  than  those  which  had  received  more  water. 
If  the  trees  had  become  so  dry  during  the  summer,  however,  that 
they  had  shown  the  effects  of  drought,  they  were  often  severely  in- 
jured by  freezing.  In  a  grove  of  young  trees  three  or  four  years  old, 
that  had  received  scant  irrigation  during  the  summer,  the  trees 
farthest  from  the  head  ditch  had  become,  before  the  freeze,  yellow- 
leafed  and  looked  as  if  they  were  dying.  These  trees  were  frozen 
to  the  ground,  but  nevertheless  most  of  the  trees  of  this  grove  were 
less  injured  than  those  in  near-by  groves  that  had  received  more 
water.  Of  course  it  would  not  be  desirable  to  keep  a  grove  dry  and 
dormant  all  summer  in  order  that  it  might  live  through  the  winter. 
These  cases  are  referred  to  merely  to  show  that  dormancy  in  some 
cases  was  induced  by  dryness,  and  that  it  is  best  not  to  give  a  young 
grove  too  much  water  in  the  fall  of  the  year. 

Irrigation. — It  was  found  that  even  when  trees  had  been  well 
supplied  with  water  during  the  summer  the  interval  that  had  elapsed 
between  the  freeze  and  the  time  of  the  previous  irrigation  frequently 
influenced  their  hardiness.  A  number  of  places  were  found  where  all 
of  the  factors  were  the  same  except  the  time  of  irrigation  and  where 
there  were  marked  differences  in  the  injury  which  the  differently 
irrigated  portions  had  sustained.  In  these  cases  the  trees  that  had 
been  irrigated  about  two  weeks  before  the  freeze  were  damaged  more 
than  trees  which  were  about  six  weeks  from  irrigation.  Even  when 
it  is  likely  that  all  of  the  trees  had  their  conducting  vessels  well  sup- 
plied with  moisture  there  was  sometimes  a  difference  in  condition 
among  these  trees  corresponding  to  the  differences  in  the  intervals 
that  had  elapsed  since  the  previous  irrigation.  To  illustrate,  in  one 
grove  water  was  running  over  the  entire  grove  at  the  time  of  the 
freeze.  Most  of  the  grove  had  not  been  irrigated  before  for  about 
six  weeks,  but  a  few  rows  at  one  side  of  the  grove  had  been  given  an 
extra  run  of  water  about  two  weeks  before  the  freeze.  These  rows 
were  much  more  damaged  than  the  rest  of  the  grove. 

While  the  number  of  conflicting  cases  observed  make  it  difficult  to 
deduce  any  general  rules,  it  seems  safe  to  conclude  that  trees  which 
were  suffering  from  lack  of  water  and  trees  that  contained  the  maxi- 
mum quantity  of  water  were  more  severely  injured  than  trees  that 
contained  a  medium  amount  of  water. 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  279 

Pruning. — It  has  been  the  practice  of  many  lemon  growers  to 
prune  in  the  fall  of  the  year.  Groves  were  found  where  trees  that 
had  been  pruned  at  this  time  were  much  more  seriously  injured  than 
unpruned  trees  which  were  under  otherwise  similar  conditions.  The 
most  severe  damage  was  to  those  trees  that  had  started  a  vigorous 
growth  as  a  result  of  the  pruning.  In  one  grove  of  young  trees,  which 
had  been  stimulated  into  growth  by  pruning,  the  bark  of  the  trunks 
and  limbs  was  badly  split.  Some  adjacent  trees  of  the  same  age  and 
similarly  located,  which  had  not  been  pruned,  were  injured  but  little. 
The  pruning  was  done  the  last  of  September,  so  that  in  this  case  there 
had  been  a  three  months '  interval  between  the  pruning  and  the  freeze. 

Where  the  cutting  had  been  done  so  late  that  no  new  growth  had 
started  there  was,  as  a  rule,  no  noticeable  difference  in  resistance  be- 
tween the  pruned  trees  and  those  which  had  not  been  pruned.  In 
one  young  grove,  however,  a  very  marked  difference  was  to  be  seen 
between  some  trees  which  were  unpruned  and  some  adjacent  rows 
where  the  pruning  had  been  discontinued  the  night  before  the  freeze. 
The  grove  consisted  of  four-year-old  Eureka  lemon  trees  and  the  cut- 
ting had  been  moderate.  There  was  a  very  marked  difference  in 
condition  between  the  section  which  had  been  pruned  and  that  which 
had  not  been  pruned.  This  difference  was  not  so  decided  immedi- 
ately after  the  freeze  as  it  was  when  the  trees  began  to  grow.  At 
this  time  the  unpruned  trees  showed  much  more  vigor  than  the  other 
trees.  The  pruning  of  the  grove  was  finished  in  the  spring  and  all 
of  the  trees  had  been  made  the  same  size,  so  that  there  was  no  differ- 
ence in  that  respect.  Any  one  in  walking  through  the  grove  could 
easily  tell  to  a  row  where  the  pruning  had  been  done  before  the  freeze. 

A  few  instances  of  late  pruning  were  found  which  resulted  -in  a 
greater  loss  of  fruit  than  in  trees  not  pruned.  This,  of  course,  is  to 
be  expected,  for  the  abundant  top  growth  affords  considerable  pro- 
tection to  the  fruit. 

Unhealthy  Trees. — Sickly  trees  were  invariably  more  severly  in- 
jured than  vigorous,  healthy  trees.  This  was  very  noticeable  in  the 
case  of  trees  suffering  from  such  diseases  as  gummosis  and  scaly  bark. 
Trees  that  had  been  badly  infested  with  insect  pests  were  damaged 
more  than  trees  which  were  in  good  health  and  free  from  pests. 
Branches  that  had  been  attacked  with  red  spider  were  completely 
killed  in  many  trees  which  suffered  only  partial  defoliation  of  the 
other  branches. 

Sometimes  healthy  trees  had  been  given  some  treatment  before  the 
freeze  that  weakened  them  and  augmented  the  frost  damage.  For 
example,  young  trees  which  had  been  scored  along  the  trunks  on  one 


280 


UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 


or  two  sides,  with  the  idea  that  by  thus  cutting  out  a  narrow  strip 
of  bark  growth  could  be  hastened,  were  much  oftener  found  with  split 
and  loosened  bark  after  the  freeze  than  trees  where  the  bark  had  been 
left  intact.  The  demonstrations  of  this  point  were  so  general  that  the 
method  of  scoring  young  trees  will  probably  not 
be  practiced  in  the  future. 

Some  ranchers  had  practiced  rubbing  neats- 
foot oil  on  the  bark  of  trees  which  were  affected 
with  gum  disease.  Occasionally  a  man  was 
found  who  had  put  this  oil  on  the  bark  of 
healthy  trees,  reasoning  that  if  neatsfoot  oil 
was  good  for  trees  suffering  with  gum  disease, 
which  it  is  not,  it  should  be  a  good  preventive 
measure.  In  some  of  these  places,  where  large 
bearing  lemon  trees  that  had  been  in  good 
health  but  had  had  the  trunks  painted  with 
neatsfoot  oil  as  a  preventive  against  gummosis, 
the  oiled  trunks  had  all  of  the  bark  killed,  while 
trunks  which  had  not  been  oiled  had  their  bark 
unharmed. 

Although  the  observations  as  to  greater  frost 
injury  to  sick  trees  were  in  most  cases  from  a 
few  isolated  trees  in  individual  orchards,  where 

the  majority  of  trees  were  healthy,  the  same 
Tig.   10. — Two-year-old  ,  ,,     ,  ,  ,     ,  ,    _,  ,. 

Eureka  lemon  on  which  general  results  have  been  noted  between  entire 

bark  had  been  slit  longi-   groves  in  the  same  section,  and  under  practi- 
tudinally     (scored)     with        ,,        ,  ,.,.  ,          .  , 

knife  before  the  freeze   cally  the  same  condition  as  to  elevation  and 

and    which    the    freeze  temperature.    Although  immediately  following 

further  seriously  injured    ,,       „  T.,-,      j-a> 

though  the  foliage  of  the   the  freeze  there  was  little  difference  in  appear- 

tree  remained  uninjured.   ance  between  groves  in  various  states  of  vigor, 
Scoring  the  bark  in  this    ,,  , .  ,.  ,,      •,       ,,, 

way   does  no   good  and   tne  greater  recuperative  powers  of  the  healthy, 

may  cause  serious  injury.   Well  cared  for,  clean  orchards  than  of  dirty, 

Photo  by  Tylor,  July  5.      .  ,  ,  -,    £  i_        i. 

1913  '   sickly,  poorly  cared  for  groves  has  been  very 

marked. 

Influence  of  Trunk-Section  of  Top-Worked  Trees. — A  very  inter- 
esting difference  which  was  brought  out  by  the  freeze  was  that  of  the 
resistance  offered  by  trees  which  had  the  same  kind  of  tops  but  dif- 
ferent kind  of  trunks.  Of  course  most  of  the  citrus  trees  have  the 
top  and  the  trunk  the  same,  as  they  are  budded  low.  But  there  are 
many  groves  in  which  the  trunk  of  the  tree  is  lemon  and  the  top 
orange,  the  trees  having  been  worked  over  from  lemons  to  oranges  at 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  281 

a  time  when  lemons  were  not  paying.  There  are  also  some  places 
where  trees  with  lemon  tops  have  orange  trunks. 

Several  places  were  found  where  young  trees  with  lemon  tops  and 
orange  trunks  were  set  among  lemon  trees  of  the  same  age  which  had 
lemon  trunks.  In  one  of  these  places  the  trees  were  all  of  the  same 
age,  having  been  set  about  one  year.  Most  of  the  trees  had  lemon 
trunks,  but  there  were  two  rows  of  trees  in  the  middle  of  the  grove 
that  had  Valencia  trunks  with  lemon  tops.  The  trees  of  the  grove 
were  uniform  in  size,  and  previous  to  the  freeze  there  was  nothing 
to  draw  one's  attention  to  the  fact  that  some  of  the  trees  in  this  young 
lemon  grove  had  orange  trunks.  After  the  freeze,  however,  any  one 
passing  this  grove  would  have  noticed  that  two  rows  in  it  differed 
in  some  important  respect  from  the  rest  of  the  trees.  For  the  trees 
with  orange  trunks  bore  branches  covered  with  green  leaves,  live 
lemon  branches  and  lemon  leaves,  but  the  other  trees  in  the  grove 
were  killed  nearly  or  quite  to  the  ground.  Four  other  places  were 
found  where  young  lemon  trees  with  orange  trunks  were  adjacent  to 
young  lemon  trees  on  their  own  trunks,  and  in  all  of  these  cases  the 
trees  with  the  orange  trunks  proved  much  hardier.  It  might  be 
thought  from  this  that  the  superior  hardiness  of  the  trees  with  orange 
trunks  is  due  to  the  well  known  greater  resistance  to  freezing  which 
orange  wood  possesses.  It  is  rather  hard  to  see  on  this  basis,  however, 
why  the  lemon  tops  of  the  trees  with  the  orange  trunks  should  have 
been  so  slightly  injured.  The  superior  resistance  of  the  trees  was 
not  confined  to  the  trunks,  for  their  lemon  tops  were  hardier  than 
the  tops  of  the  trees  with  lemon  trunks.  It  is  clear  that  the  trunks 
of  these  trees  had  influenced  the  tops  and  had  increased  their  hardi- 
ness. This  probably  means  that  in  some  way  the  trunks  of  the  trees 
modified  the  dormancy  of  the  tops. 

Not  many  bearing  groves  have  been  worked  over  from  oranges  to 
lemons,  so  that  it  has  not  been  possible  to  find  many  comparisons 
between  such  groves  and  bearing  lemon  trees  on  their  own  trunks. 
Some  bearing  lemon  trees  with  orange  trunks  were  found,  and  also 
some  bearing  lemons  which  had  tangerine  trunks,  but  these  trees  did 
not  seem  to  be  strikingly  hardier  than  ordinary  lemon  trees. 

It  was  much  easier  to  find  bearing  orange  groves  where  the  trees 
in  parts  of  the  grove  had  lemon  trunks.  Such  groves  are  rather 
common  in  southern  California  because  about  ten  years  ago  there 
was  such  a  depression  in  the  lemon  market  that  many  growers  budded 
their  lemon  trees  over  to  oranges. 

In  some  places  these  orange  trees  with  lemon  trunks  were  injured 
much  more  than  adjacent  orange  trees  on  their  own  trunks.  One 

21P384 

UiViSION  OF  SUBTROPICAL  HORTICULTURE 
COLLEGE  OF  AGRICULTURE 


282  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

grove  of  navel  oranges  was  found  where  every  other  tree  in  the  row 
had  a  lemon  trunk.  In  parts  of  this  grove  the  trees  with  the  lemon 
trunks  had  lost  two  or  three  times  as  many  leaves  as  the  trees  with 
the  orange  trunks.  Numerous  other  cases  were  found  where  orange 
trees  with  lemon  trunks  were  injured  more  than  similarly  situated 
trees  with  orange  trunks,  but  the  reverse  of  this  sometimes  occurred, 
so  that  no  positive  rule  can  be  stated.  It  is,  however,  pretty  clearly 
evident  that  it  is,  in  general,  poor  policy  to  top  work  lemons  to  oranges. 

Influence  of  Roots  or  Stocks. — It  has  been  claimed  that  the  root- 
stock  on  which  the  tree  is  budded  may  affect  the  resistance  of  the  top. 
The  stocks  that  have  been  most  used  in  California  are  the  sweet  orange 
and  the  sour  orange.  In  general,  no  difference  in  the  resistance  of 
the  trees  on  these  two  stocks  could  be  found. 

In  one  rather  large  nursery,  containing  both  sweet  and  sour  seed- 
lings, all  the  trees  were  killed  to  the  ground  in  January,  but  on 
June  12, 1913,  a  count  of  several  hundred  trees  of  each  variety  showed 
that  71.3  per  cent  of  the  sweet  and  71.2  per  cent  of  the  sour  trees 
were  recovering,  and  new  sprouts  several  inches  long  were  growing 
from  the  young  trunks  near  the  surface  of  the  ground. 

Comparative  Resistance  of  Sweet  and  Sour  Stock 


Sweet  Orange 

Number  trees 
counted 

882 

Number  trees 
producing 
new  sprouts 

629 

Per  cent  trees 
recovering 
from  freeze 

71.3 

Sour  Oranare  ... 

795 

566 

71.2 

Pomelo  stock  has  been  used  by  many  growers,  but  no  cases  were 
found  where  the  trees  on  this  stock  were  noticeably  different  from 
those  on  other  stocks. 

In  one  young  lemon  grove  the  trees  on  trifoliate  orange  roots  were 
hardier  than  the  trees  on  sour  orange  roots.  At  least  one  case  was 
observed  in  California  where  navels  on  trifoliate  stock  appeared  to 
be  distinctly  less  injured  than  navels  on  sweet  stock  planted  at  the 
same  time  and  in  the  same  grove  and  having  the  same  treatment. 
In  general,  it  may  apparently  be  concluded  that  the  trifoliate  stock 
has  a  tendency  to  render  orange  budded  on  it  rather  more  hardy,  but 
that  the  difference  is  slight. 

In  some  cases  there  is  apparently  a  definite  influence  of  the  tops 
upon  the  stocks.  In  one  case,  in  the  spring  of  1912,  a  nursery  of  sour 
seedlings  was  budded  to  Eureka  lemons.  Many  of  these  buds  did 
not  take,  so  that  during  the  freeze  of  January,  1913,  there  were  in 
this  nursery,  at  the.  same  elevation  and  under  the  same  conditions, 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  283 

yearling  lemon  tops  on  sour  stock  (buds  had  been  inserted  several 
inches  above  the  ground)  alongside  of  sour  seedlings.  While  a  slight 
injury  to  the  foliage  was  the  only  harm  experienced  by  the  latter, 
the  lemon  tops  were  killed,  and  the  frozen  wood  extended  three  to 
four  inches  down  on  the  sour  stock.  Similar  conditions  were  found 
on  pomelo  stock,  while  the  pomelo  seedlings  were  scarcely  touched. 

Individuality  of  Trees. — One  of  the  most  pronounced  features  of 
the  freeze  was  the  greater  resistance  of  some  individual  trees  to  frost 
injury  than  of  other  trees,  of  the  same  age  and  kind  and  growing 
under  the  same  conditions.  This  perhaps  was  more  apparent  in  young 
orchards  than  in  old  ones,  and  many  instances  have  been  seen  in  which 
the  majority  of  trees  in  a  young  lemon  grove  have  been  killed  to  the 
bud,  while  here  and  there  scattered  irregularly  through  the  grove 
were  individual  trees  retaining  a  certain  proportion  of  green  foliage. 
The  same  individuality  of  trees  occurs  in  old  groves,  but  is  not  always 
so  well  defined. 

In  no  case  was  it  possible  to  determine  whether  the  escape  of 
these  trees  from  injury  was  due  to  accidental  conditions,  rendering 
such  trees  more  dormant  and  thus  more  resistant,  or  whether  due  to 
inherent  frost-resistant  qualities. 

TREATMENT  OF  FROZEN  TREES 

Soon  after  the  freeze  it  became  apparent  that  the  citrus  groves 
had  been  very  seriously  injured  and  growers  were  confronted  with 
many  important  problems  connected  with  their  rejuvenation.  No 
experience  was  available  to  serve  as  a  guide,  and  thus  many  different 
methods  were  tested  that  appeared  to  give  promise  of  value.  The 
trees  given  these  different  treatments  were  watched,  and  it  has  been 
possible  to  reach  definite  conclusions  regarding  the  value  of  most  of 
the  practices  which  followed  the  freeze. 

Binding  Loose  Bark. — In  many  places  where  loose  bark  was  bound 
back  to  the  tree  again  apparently  nothing  was  gained,  for  the  loosened 
bark  died.  Many  growers,  however,  reported  that  they  had  trees  the 
bark  of  which  was  loose  immediately  after  the  freeze  but  which  later 
reunited  with  the  wood. 

Considerable  uncertainty  exists  regarding  most  of  these  reports, 
but  it  is  probable  that  some  of  them  are  true,  inasmuch  as  there  were 
many  examples  where  the  bark  had  split  and  separated  from  the  tree 
without  being  killed.  This  bark  not  only  remained  alive  but  devel- 
oped a  layer  of  wood  on  its  inner  surface,  and  a  new  bark  was  devel- 
oped next  to  the  wood  of  the  tree. 


284  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

Some  trees  were  found  which  clearly  showed  that  such  an  occur- 
rence actually  took  place.  The  bark  on  the  north  side  of  a  three- 
year-old  lemon  tree  had  been  longitudinally  split  and  had  separated 
from  the  wood  for  an  inch  and  a  half  or  so  on  each  side  of  the  split. 
At  one  place  it  had  been  tied  down  to  the  tree  again  by  a  piece  of 
twine,  which  brought  the  wood  and  bark  together  at  this  place  only. 
Both  above  and  below  the  twine  the  bark  had  remained  separated  from 
the  tree.  The  bark  was  not  killed,  and  where  it  had  been  tied  it  had 
reunited  firmly  with  the  tree. 


Fig.  11. — Cross  section  of  young  lemon  trunks  on  which  bark  was  split 
by  freezing,  showing  the  injury  to  the  wood  which  is  dead  back  to  the  inked 
lines.  New  wood  can  be  seen  forming  on  the  loose  ends  of  the  bark  which 
was  not  killed. 

In  many  cases  where  split  trees  were  wrapped  the  process  was  so 
thoroughly  done  that  the  moisture  was  held  in  and  molding  favored. 
The  best  instances  of  recovery  from  wrapping  were  those  where  cord, 
like  binding  twine,  or  narrow  strips  of  cloth  were  wrapped  around 
the  tree  spirally,  leaving  the  greater  portion  of  the  bark  uncovered 
and  allowing  the  free  access  of  the  air,  but  holding  the  loose  bark 
firmly  against  the  wood.  Such  wrapping  to  have  any  effect  must 
be  done  promptly  after  a  freeze,  while  the  injured  surfaces  of  bark 
and  wood  are  fresh,  otherwise  the  wrapping  naturally  could  have  no 
beneficial  effect.  Where  bark  is  split  and  loosened  it  is  likely  to  bend' 
outward  a.3  it  dries  and  exert  a  force  that  will  have  a  tendency  to 
extend  the  injured  area.  Binding  with  cord  as  indicated  will  prevent 
such  extension  of  the  injury  and  favor  the  bark  healing  on,  while 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA 


285 


it  is  not  too  severely  injured.  In  many  cases  where  no  beneficial 
results  were  observed  from  wrapping  the  treatment  was  applied  too 
late,  or  the  injury  was  so  severe  that  no  treatment  could  be  effective 
in  saving  the  injured  parts  (fig.  12). 
Where  trees  are  treated  in  this 
way  following  a  freeze  they  should 
be  given  no  other  treatment,  unless 
the  trunks  are  whitewashed  to  pro- 
tect them  from  sunburning.  No 
further  treatment  than  the  wrapping 
is  necessary  for  several  months,  or 
until  the  new  growth  is  well  under 
way  and  until  bark  that  was  killed 
has  dried  out  and  clearly  shows  the 
extent  of  the  damage.  As  soon  as 
this  time  arrives,  the  wrappings 
should  be  removed,  the  dead  bark 
thoroughly  cut  away,  and  the  in- 
jured patches  thoroughly  cleaned. 
After  this  cleaning,  probably  the  best 
treatment  is  to  first  paint  the  injured 
area  with  Bordeaux  paste  and  some 
weeks  later  with  asphalt  dissolved  in 
benzine.  The  use  of  Bordeaux  paste 
as  a  first  treatment  seems  to  be  very 
desirable,  as  it  seems  necessary  to 
use  some  sterilizing  solution  to  pre- 
vent the  development  of  fungi.  Fol- 
lowing this  treatment  with  a  coating 
of  asphalt  paint  renders  the  wound 
impervious  to  wrater  and  gives  a  per- 
manent finish  to  the  treatment. 

Waxing  and  Painting  Split  Bark. 
—The  covering  of  the  splits  in 
the  bark  with  grafting  wax  was 
a  very  common  practice.  Some 
growers  used  white  lead  instead  of  wax.  Sometimes  the  bark  was 
wrapped  after  the  waxing,  and  sometimes  the  waxing  was  the  only 
treatment  given.  Where  there  was  a  chance  to  compare  waxed  trees 
with  those  that  had  not  been  treated,  there  was  nothing  to  show  that 
the  waxing  had  done  good.  It  was  practically  impossible  to  get  the 
wax  under  the  loose  bark,  and  so  the  wax  simply  sealed  up  moist 


Fig.  12. — Four-year-old  Eureka 
lemon,  on  which  the  split  bark  was 
covered  with  grafting  wax  and 
wrapped  with  twine.  Treatment  ap- 
parently did  no  good  because  of 
grafting  wax.  Loosened  bark  prompt- 
ly wrapped  with  twine  without  other 
treatment  frequently  healed  on.  Photo 
by  Tylor. 


286 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


chambers  which  offered  most  favorable  conditions  for  the  growth  of 
fungi.  Even  where  the  wax  was  put  on  before  there  was  much  loos- 
ening of  the  bark,  it  did  little  good  because  the  later  loosening  and 
curling  of  the  bark  cracked  it  (fig.  12). 

White  lead,  applied  by  painting  the  cracks  soon  after  the  freeze, 
proved  no  more  valuable  than  wax,  and  no  places  were  found  where 
trees  were  in  any  way  benefited  by  having  the  trunks  wrapped  in 


Fig.  13.— Badly  injured  Eureka  lemon  tree,  unpruned,  five  and  one-half 
months  after  freeze,  showing  the  extent  of  damage  and  the  new  growth 
that  has  developed.  Trees  at  the  stage  shown  in  this  illustration  can  be 
pruned  to  advantage,  all  of  the  dead  wood  being  removed  at  one  time. 
Photo  June  24,  1913,  by  Tylor.  (This  tree  was  immediatley  beside  that 
shown  in  fig.  14.) 

cow  dung.    Some  cases  have  been  reported,  however,  where  gummosis 
was  started  by  this  treatment. 

Pruning  Injured  Trees. — One  of  the  most  important  operations 
necessitated  by  the  freeze  was  pruning.  It  was  maintained  by  some 
that  prompt  pruning  was  very  necessary  in  order  to  prevent  a  further 
dying  back  of  the  frozen  wood.  This  dying  back  would  be  caused,  it 
was  claimed,  by  a  backward  passage  of  sour  sap.  However,  difficulty 
was  experienced  in  telling  soon  after  the  freeze  where  the  uninjured 
portions  of  wood  began.  So  when  it  was  advised  on  the  special  Frost 


EFFECTS  OF  FREEZES  ON  CITRUS  IX  CALIFORNIA 


L>>7 


Train,  run  by  the  College  of  Agriculture  of  the  University  that  it 
would  be  better  to  wait,  whenever  the  damage  had  been  at  all  severe, 
until  the  extent  of  the  damage  became  clearly  defined,  the  majority  of 
the  growers  adopted  this  policy. 

The  effect  of  early  and  late  pruning  was  easily  observed  and. was 
tested  out  by  many  growers.  The  following  two  instances  may  be 
cited  as  definite  experiments.  In  one  orchard  of  old  lemon  trees  a 


Fig.  14. — Badly  injured  Eureka  lemon  tree,  pruned  February  1,  1913, 
and  photographed  four  and  one-half  months  later,  showing  the  dicing  back 
of  large  limbs  after  the  first  pruning.  Such  early  pruned  trees  as  this 
made  no  better  growth  than  unpruned  trees  and  required  a  second  pruning. 
Photo  by  Tylor  June  24,  1913  (compare  fig.  13.) 

certain  portion  of  the  trees  were  cut  back  in  February,  and  all  wood 
at  that  time  thought  to  be  dead  was  cut  out.  A  check  row,  however, 
was  left,  which  was  not  pruned  until  summer.  The  cuts  made  during 
February  were  in  most  places  on  wood  that  ultimately  died.  In  this 
case  there  was  no  apparent  difference  in  amount  of  new  growth 
produced  on  the  trees  under  the  different  treatments,  but  in  the  case 
of  the  early  pruning,  a  second  cutting  was  necessary  in  order  to 
completely  remove  all  the  dead,  frozen  branches  (figs.  13  and  14). 
In  an  experiment,  carried  out  by  the  Citrus  Experiment  Station 


288  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

through  the  kindness  of  the  Arlington  Heights  Fruit  Company,  seven- 
year-old  lemon  trees  that  were  rather  severely  injured  were  pruned 
in  several  different  ways.  About  ten  trees  were  treated  by  each 
method,  the  pruning  being  done  about  the  middle  of  March,  1913, 
thus  somewhat  over  two  months  after  the  freeze.  Kow  1  was  left 
entirely  unpruned.  In  row  2  the  trees  were  pruned  moderately, 
limbs  being  removed  as  far  back  as  they  were  thought  to  be  injured. 
In  row  3  without  reference  to  injury,  the  trees  were  cut  back  to  the 
principal  branches,  thus  being  very  severely  pruned.  In  row  4  the 
trees  were  cut  off  below  the  crown,  leaving  thus  only  the  trunks. 

No  further  pruning  was  given  until  May,  1914.  At  this  time  it 
was  clearly  evident  that  row  1,  unpruned,  and  row  2,  lightly  pruned, 
had  developed  the  largest  tops  and  the  most  fruit,  there  being  no  fruit 
on  the  other  rows.  The  dead  branches  on  row  1  had  up  to  this  time 
caused  no  injury  and  could  be  easily  distinguished  and  removed. 
The  growth  on  these  trees  after  pruning  seemed  to  be,  as  a  whole, 
better,  more  vigorous,  and  more  fruitful  than  on  any  other  row, 
though  scarcely  any  better  than  row  2.  Eow  2,  however,  required 
a  second  severe  pruning,  the  treatment  thus  being  much  more  expen- 
sive than  the  one  pruning  given  row  1.  The  pruning  in  rows  3  and  4 
had  clearly  been  too  severe  to  give  the  best  results. 

The  treatment  of  limbs  on  which  large  patches  of  bark  were  killed 
is  very  perplexing.  Where  a  limb  was  partially  girdled,  it  was  a 
question  how  wide  a  strip  of  living  bark  it  should  have  in  order  to 
give  satisfactory  growth.  No  positive  directions  can  be  given  regard- 
ing such  variable  cases,  as  judgment  must  be  used  in  every  case.  It  is 
thought,  in  general,  that  where  a  limb  is  more  than  half  girdled,  it 
would  be  better  to  remove  it  and  allow  a  strong  new  branch  to  take 
its  place. 

It  must  be  remembered  that  in  pruning  frozen  trees,  it  is  highly 
important  to  treat  the  large  cut  surfaces  with  a  fungicide,  such  as 
Bordeaux  paste  or  Bordeaux  mixture,  followed  with  asphalt  paint. 

The  results  obtained  in  these  experiments  correspond  entirely  with 
the  experience  of  growers  all  over  the  state,  and  demonstrated  con- 
clusively that  early  pruning  after  a  freeze  is  unnecessary,  does  no 
good,  and  increases  the  expense,  as  a  second  pruning  is  necessitated. 
It  may  do  damage  to  some  extent,  by  causing  sunburning.  Far  the 
best  method  is  to  delay  the  pruning  for  from  five  to  six  months  or 
longer,  until  the  trees  have  had  time  to  throw  out  new  growth  and 
plainly  delimit  the  dead  portion.  All  necessary  pruning  can  then  be 
done  at  one  time.  The  early  pruning  of  lightly  frozen  trees,  in  lemons 
especially,  is  likely  to  remove  uninjured  fruit  wood  and  lessen  the 
following  crop. 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  280 

The  early  pruned  nursery  stock  was  found  to  be  slower  in  starting 
growth  than  unpruned  stock,  a  delay  of  as  much  as  three  weeks  being 
observed  in  some  cases. 

Many  growers  did  not  attempt  to  remove  the  small  frozen  twigs  in 
lightly  injured  trees.  Leaving  this  dead  brush  in  the  tree  was  found 
to  increase  the  amount  of  fruit  spotting,  and  decay  the  next  year. 

Removing  Frozen  Fruit. — As  soon  as  it  was  learned  that  the  fruit 
had  been  frozen,  some  growers  had  it  promptly  removed.  This  cost 
for  oranges  from  five  to  ten  cents  per  tree  on  the  average,  while  some 
lemon  growers  had  to  pay  as  much  as  twenty  cents  per  tree. 

Experience  demonstrated  that  there  is  no  need  of  haste  in  removing 
frozen  fruit,  unless  it  is  to  be  used  for  making  by-products.  Some 
of  the  frozen  fruit  will  drop  of  its  own  accord  and  if  wood  injury 
necessitates  pruning  much  of  the  old  fruit  will  be  removed  by  this 
operation.  What  remains  can  be  pulled  off  later  at  any  convenient 
period.  There  was  no  evidence  obtained  indicating  that  the  succeed- 
ing crop  was  injured  by  this  frozen  fruit  remaining  on  the  tree,  other 
than  the  injury  that  may  result  from  the  spreading  of  fungus  spores 
from  the  old  fruit,  thereby  increasing  spotting  in  the  next  crop. 

Whitewashing  Exposed  Trunks. — Where  trees  were  defoliated, 
many  growers  felt  that  the  bark  should  be  protected  in  some  way 
from  the  burning  action  of  the  sun.  The  most  feasible  way  to  do 
this  was  to  whitewash  the  trees,  and  this  was  done  in  many  cases. 
Where  the  whitewash  was  put  on  before  any  new  growth  had  started, 
the  appearance  of  the  new  growth  was  delayed  about  three  weeks. 
When  the  application  was  not  made  until  after  the  growth  had  started, 
the  tender  leaves  were  sometimes  injured.  The  whitewash  was  always 
cooled  before  using  it,  but  there  were  many  examples  where  after  it 
had  cooled  over  night,  it  injured  tender  growth.  Where  it  was  allowed 
to  stand  a  week  before  being  put  on,  it  had  no  injurious  effects. 

In  case  there  are  but  a  few  trees  to  be  treated,  the  whitewashing 
of  bare  trunks  and  limbs  can  be  done  with  a  brush,  but  on  the  larger 
ranches,  the  most  economical  system  is  to  make  a  thin  wash  that  will 
go  through  a  spray  nozzle  and  apply  it  by  means  of  a  power  spray 
pump.  (See  formula  below.*) 

The  Renewal  of  Badly-Injured  Young  Trees. — Young  lemon  and 
orange  trees  suffered  various  degrees  of  injury,  but  were  much  more 
generally  and  severely  injured  than  older  trees.  Severe  cases  of  sun- 


*  Formula  for  California  Whitewash:  Take  30  pounds  of  quick  lime,  4  pounds 
of  tallow,  5  pounds  of  salt,  and  mix  together,  slake  slowly  and  blend.  Dilute  with 
enough  water  to  make  mixture  flow  well. 


290 


UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 


burning  frequently  resulted  on  the  south  side  of  defoliated  young 
lemon  trees  in  particular  and  the  whitewashing  of  the  trunks  of  such 
trees  soon  after  a  freeze  is  important. 

Aside  from  whitewashing,  there  seems  to  be  but  one  fixed  rule, 

and  that  is  to  let  the  trees  alone  until  the 
new  growth  is  well  under  way,  and  the 
demarcation  between  dead  and  living  wood 
has  become  plainly  apparent. 

The  method  of  renewal  of  young  trees 
depends  entirely  on  the  degree  of  injury. 
If  the  trees  have  lost  only  a  portion  of 
their  heads,  a  new  head  may  be  shaped 
after  the  growth  is  well  under  way.  With 
trees  that  lost  their  entire  crowns  but  re- 
tained sound  trunks,  as  happened  in  many 
cases  especially  where  they  had  been  pro- 
tected by  a  wrap  during  the  freeze,  it 
proved  to  be  thoroughly  practical  to  train 
three  or  four  sprouts,  properly  located 
and  spaced  near  the  top  of  the  trunk,  to 
form  the  new  head. 

If  the  trunk  is  killed  too  far  down  to 
produce  a  good-shaped  head,  but  is  still 
living  above  the  bud,  the  best  method  of 
renewal  is  to  select  a  strong  sprout  that 
springs  out  above  the  bud  and  train  it 
into  a  new  tree,  retaining  the  old  trunk 
as  a  supporting  stake  until  the  sprout 
becomes  strong  enough  to  need  no  support. 
Remove  all  other  sprouts  and  throw  the 
full  strength  of  the  tree  into  this  one 
sprout.  Many  young  sprouts  that  did  not 
even  start  growing  until  the  middle  or 
latter  part  of  March,  trained  in  this  man- 
ner and  headed  before  the  August  growth, 
in  seven  or  eight  months  made  splendid 
vonng  trees,  better  than  new  trees  planted 

m  the  spring.  Whatever  system  of  renewing  young  trees  is  followed, 
it  is  important  to  start  below  all  large  areas  of  dead  wood.  There  is 
too  much  at  stake  to  grow  a  new  tree  for  several  years  on  a  rotten 
foundation.  If  the  main  crotch  has  been  badly  frozen  and  the  dead 
bark  and  wood  extends  downward  from  this  injury,  sacrifice  the  top 
and  start  the  new  head  from  healthy  tissue  (fig.  15). 


Fig.  15.— The  develop- 
ment of  a  new  tree  from  a 
sprout  springing  from  base 
of  trunk  above  the  bud,  the 
old  trunk  being  retained  for 
a  time  as  a  stake  for  the 
new  tree.  Photo  by  Tylor, 
September  6,  1913. 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  291 

Grafting  or  Budding  Badly-Injured  Trees. — Where  trees  were 
frozen  down  to  the  bud,  one  of  three  things  was  done :  the  trees  were 
uprooted  and  thrown  away;  or  they  were  allowed  to  send  out  new 
shoots,  one  of  which  was  budded ;  or  they  were  cut  off  and  grafted. 
Grafting  was  successful  in  some  places,  and  failed  in  others.  The 
two  methods  used  were  cleft-grafting  and  crown-grafting.  Where  the 
tree  was  one  or  two  inches  in  diameter,  it  was  sawed  off  down  to  good 
live  wood,  was  split,  and  then  two  wedge-shaped  scions  were  put  in 
by  the  cleft-graft  method,  one  on  each  side,  so  that  the  cambium  of 
the  scion  came  next  to  the  cambium  of  the  stock.  Where  the  trees 
were  so  large  that  they  could  not  easily  be  split  in  this  way,  a  stick 
of  bud-wood  with  one  end  cut  diagonally  was  placed  between  the  bark 
and  the  wood,  with  the  cut  surface  next  to  the  wood.  The  failures 
were  caused  mainly  by  the  drying  out  of  the  scions  before  they  had 
united  with  the  stocks,  or  by  the  dying  back  of  the  stock  below  the 
place  where  the  scion  was  inserted.  Grafting,  in  general,  proved 
unsatisfactory. 

The  most  successful  method  pursued  was  to  train  up  a  vigorous 
sprout  from  the  stock  which  was  budded  in  the  summer  as  soon  as  it 
had  reached  sufficient  size. 

Irrigation  to  Aid  Recovery  of  Frozen  Fruit. — It  was  thought  by 
some  people  that  fruit  which  had  been  partly  frozen  would  recover 
if  the  conditions  were  favorable,  and  that  frequent  irrigation  would 
assist  in  this  recovery.  Irrigation  was  given  a  fair  trial  in  several 
cases  with  Valencias  and  navels,  but  the  fruit  was  not  benefited, 
showing  no  improvement  over  adjacent  groves  which  were  not  irri- 
gated. In  fact,  no  places  were  found  where  there  was  any  recovery 
of  fruit  after  February  1  which  was  of  any  commercial  importance. 
Some  frozen  lemons  were  examined  in  which  it  looked  as  if  new  pulp 
cells  had  formed  next  to  the  skin,  but  this  was  not  general  enough  nor 
extensive  enougli  to  need  consideration  commercially.  Instead  of 
any  recovery  taking  place  in  frozen  fruit,  there  was  a  steady  deteriora- 
tion the  older  it  grew. 

Stimulating  Growth  in  Frozen  Trees  by  Fertilization. — Many 
growers  following  the  1913  freeze  gave  their  trees  extra  applications 
of  nitrate  of  soda  and  other  quick-acting  fertilizers,  thinking  thereby 
to  stimulate  more  rapid  growth  and  cause  the  flowers  to  set  more 
fruit.  Little  or  no  benefit  was  derived  from  such  extra  applications, 
though  no  harm  was  done,  as  has  sometimes  followed  in  Florida.  The 
omitting  of  all  fertilization,  however,  was  very  clearly  a  mistake, 
unless  the  freezing  had  been  so  severe  as  to  kill  all  or  the  greater 
portion  of  the  tops,  or  in  cases  where  the  grove  had  been  highly  ferti- 
lized a  short  time  preceding  the  freeze. 


292  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

Treatment  of  Wounds  on  Frozen  Trees. — Reference  has  been  made 
in  various  places  to  the  necessity  of  properly  treating  wounds  on 
frozen  trees,  both  in  the  case  of  areas  injured  by  the  freeze  and  of 
wounds  caused  in  pruning.  In  several  sections  of  the  state,  wood 
rots  were  spread  in  the  pruning  and  apparently  caused  considerable 
damage.  In  almost  all  cases  some  material  was  used  by  growers  to 
cover  cut  .surf  aces,  such  as  grafting-wax  applied  warm,  liquid  grafting- 
wax,  white  lead,  or  some  sort  of  paint.  It  was  found  by  Dr.  Barrett 
and  Professor  Fawcett  that  these  did  not  stop  the  infection  with  the 
wood  rots  spread  by  pruning.  These  fungi  developed  under  the  wax 
or  paint.  In  the  treatment  of  the  wounds,  in  case  of  trunk  injuries 
and  comparatively  large  cut  surfaces  in  pruning  (limbs  one-half  inch 
or  more  in  diameter),  the  best  treatment  that  can  now  be  suggested 
is  painting  these,  when  freshly  cut,  with  Bordeaux  mixture  or  Bor- 
deaux paste*  and  a  few  days  later  following  this  by  painting  the  cut 
surfaces  with  asphaltum  dissolved  in  benzine,  which  gives  a  hard 
smooth  finish  that  will  last  for  a  long  period.  Asphalt  paint  dissolved 
in  benzine  (use  no  turpentine)  can  be  purchased  at  paint  stores. 


AFTER  EFFECTS  OF  THE  FEEEZE 

For  six  weeks  or  so  after  the  freeze,  there  were  no  changes  in  the 
appearance  of  the  groves,  which  could  be  looked  upon  by  the  rancher 
as  encouraging  signs.  During  this  time  the  injury  done  to  the  bark 
became  more  apparent  day  by  day:  green  bark  became  dull  in  color 
and  then  dark  brown ;  cracks  opened  wider ;  and  the  leaves  kept  falling 
except  in  some  places  where  the  freezing  had  been  most  severe.  In 
these  places  the  dead  leaves  did  not  drop  but  remained  hanging  as  if 
they  were  frozen  on. 

Appearance  of  New  Growth. — Toward  the  latter  part  of  February, 
however,  the  buds  began  to  start,  and  new  growth  appeared  in 
abundance.  This  growth  was  not  confined  to  parts  of  the  tree  which 
showed  no  injury.  Of  course,  there  was  much  wood  upon  which  no 
new  growth  appeared,  but  new  shoots  sprang  out  from  many  branches 
and  trunks,  which  were  so  badly  split  that  the  owners  were  greatly 

*  Bordeaux  paste  formula:  Dissolve  1  pound  of  bluestone  (copper  sulfate)  in 
1  gallon  of  water  in  a  wooden  or  earthen  vessel.  This  can  best  be  done  by  hanging 
it  in  a  sack  in  the  top  of  the  water.  Slake  two  pounds  of  quicklime  in  about 
one-half  gallon  of  water.  Some  variation  from  these  proportions  may  be  made 
without  greatly  changing  the  value  of  the  paste.  Stir  together  when  cool,  making 
a  light  blue  mixture  about  the  consistency  of  whitewash.  If  the  mixture  turns 
to  some  other  color  before  being  applied,  it  is  an  indication  that  something  is 
wrong.  Mix  up  fresh  each  day  or  two,  as  the  mixed  paste  tends  to  deteriorate  with 
age.  It  may  be  applied  with  a  large  brush  as  whitewash. 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  293 

surprised  to  see  them  putting  out  such  an  abundant  and  vigorous 
growth. 

Dying  of  New  Growth. — After  this  growth  had  become  a  few  inches 
long,  much  of  it  began  to  droop  and  die.  A  few  weeks  later  many 
young  trees,  which  had  started  out  with  promise,  were  entirely  dead, 
and  other  trees  kept  weakening  and  dying  throughout  the  summer. 
Sometimes  some  of  the  new  growth  would  droop  and  die  because  of 
overcrowding.  Frequently  when  two  or  three  shoots  sprang  from  the 
same  place,  all  would  continue  to  grow  until  six  to  ten  inches  long, 
and  then  one  or  two  of  these  would  droop,  become  loose,  and  fall  out, 
leaving  one  strong  sprout.  Where  there  were  these  fatal  effects  of 
overcrowding,  the  trees  were  doubtless  in  a  weakened  condition. 
Orange  trees  that  were  merely  defoliated  sent  out  a  strong  and  abun- 
dant growth  along  the  trunk  and  the  main  limbs  of  the  trees.  This 
growth  had  large  leaves  of  good  color  and  bore  strong  vigorous 
flowers.  The  leaves  that  came  out  near  the  surface  of  these  trees 
were  generally  small  and  often  variegated.  This  variegated  color  was 
plentiful  in  groves  which  had  previously  been  free  from  "mottled 
leaf." 

Where  the  bark  was  split,  the  loosened  bark  usually  curled  and 
died,  leaving  an  elliptical  patch  of  uncovered  dead  wood.  The  sound 
bark  surrounding  this  area  began  to  grow  in  from  all  sides  and  cover 
this  bare  wood  the  same  as  in  the  healing  of  any  wound. 

After  two  or  three  months,  trees  which  had  been  exposed  to  the 
lowest  temperatures  began  to  show  dead  patches  of  bark  on  some  of 
the  big  limbs.  These  patches  were  not  conspicuous,  but  could  be 
located  by  scraping  off  the  outer  surface  of  the  bark.  The  scraping 
revealed  the  brown  areas,  surrounded  by  bark,  which  was  green  and 
alive.  It  was  rare  to  find  bearing  trees  ten  years  old  or  older,  even 
in  the  districts  which  suffered  most,  where  the  trunks  of  the  trees 
showed  much  injury. 

Blooming  and  Fruiting  of  Injured  Trees. — Slightly  defoliated 
orange  trees,  even  though  the  crop  had  been  a  total  loss,  in  many  cases 
set  a  larger  crop  than  normal.  Orange  trees  that  had  been  entirely 
defoliated  in  January  produced  bloom  in  March  and  April,  a  large 
portion  of  which  was  small  and  dropped.  During  this  time  strong, 
vigorous  growth  was  developing  on  the  large  limbs  within  the  tree  and 
fruit  developed  on  this  newly  formed  growth.  The  crop  of  these 
trees,  which  had  been  entirely  defoliated  and  badly  injured  in  Janu- 
ary, was  found,  to  the  astonishment  of  many,  to  equal  in  many  cases 
40  to  60  per  cent  of  normal. 

Lemon  trees  that  had  suffered  but  slight  frost  injury  to  the  fruit, 


'TTPTCTIT/TTTRF 


294  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

in  many  cases  set  a  heavy  new  crop.  In  many  instances  it  was  found 
that  lemon  trees,  entirely  defoliated  in  January,  produced  consider- 
able bloom  in  the  spring,  but  a  large  proportion  of  this  dropped.  The 
amount  of  fruit  on  the  lemon  trees  in  the  fall  was  proportional  to  the 
amount  of  fruit-wood  not  killed  during  January.  Where  the  trees 
were  killed  back  to  the  framework  or  to  branches  one  or  two  inches 
in  diameter  there  was  no  bloom  for  twelve  months  after  the  freeze, 
although  much  new  growth  was  produced. 

The  devastation  wrought  by  the  freeze  was  so  severe  that  growers 
feared  that  no  crop  would  be  produced  the  next  year.  In  this  they 
were  fortunately  mistaken.  In  the  case  of  orange  trees  where  the 
injury  was  not  too  .severe,  the  check  to  the  vegetative  development 
apparently  acted  like  girdling  and  stimulated  a  heavy  bloom  and  set 
of  fruit.  It  is  interesting  to  note  that  similar  conditions  followed  the 
1886  freeze  in  Florida,  which  was  about  of  equal  severity  with  the 
1913  freeze  in  California.  The  Florida  crop  of  oranges  the  year  fol- 
lowing this  freeze  was  larger  than  the  crop  of  the  year  preceding  the 
freeze  (see  table  3). 

TABLE  3.— FLORIDA  CITRUS  FRUIT  CROP  FROM  1884-85  TO  1888-89 

Oranges, 
Season  boxes 

1884-85  600,000 

1885-86  900,000 

1886-87  (freeze  Jan.  12,  1886)  1,260,000 

1887-88  1,450,000 

1888-89  1,950,000 

Nearly  the  same  conditions  followed  the  California  freeze,  as  will 
be  seen  from  a  comparison  of  the  shipments  of  oranges  and  lemons 
for  the  years  preceding  and  following  the  crop  year  of  1912-13  (see 
table  4). 

TABLE  4. — SHIPMENTS  OF  CITRUS  FRUIT  FROM  CALIFORNIA,  1909-10  TO  1917-18 

Carloads  Boxes  (approximate) 


Orange 

Lemon 

Total 

Orange 

Lemon 

Total 

1909-10 

11,300,246 

1,516,021 

12,876,267 

1910-11 

39,360 

6,721 

46,081 

15,575,631 

2,256,066 

17,831,697 

1911-12 

33,671 

6,104 

39,775 

13,319,002 

2,241,990 

15,560,992 

1912-13 

17,432 

2,806 

20,238 

6,908,084 

1,117,940 

8,026,024 

1913-14 

42,706 

2,848 

45,554 

16,957,335 

1,202,964 

18,160,299 

1914-15 

40,986 

6,658 

47,644 

16,336,433 

2,639,296 

18,975,729 

1915-16 

37,336 

7,319 

44,655 

15,169,559 

2,945,589 

18,115,148 

1916-17 

45,723 

8,107 

53,830 

19,702,443 

3,312,042 

23,014,485 

1917-18 

19,506 

5,823 

25,329 

8,940,820 

2,452,481 

11,393,301 

(Cars  of  varying  capacity.) 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  295 

Several  factors  contributed  to  make  the  crop  of  1913-14  appear 
larger  than  it  really  was  in  comparison  with  preceding  crops.  The 
crop  of  1911-12  was  reduced  by  the  loss  of  considerable  fruit  through 
the  Christmas  freeze  of  1911.  The  crop  of  1912-13  was  largely 
destroyed  by  the  great  freeze.  There  had,  therefore,  been  two  years 
without  a  normal  crop.  Meanwhile,  very  extensive  areas  of  young 
plantings  had  reached  bearing  age,  and  served  to  greatly  increase  the 
crop  of  1913-14.  There  were  many  acres  of  old,  bearing  trees  and 
trees  of  all  ages,  where  the  crop  wras  very  greatly  reduced  by  the 
freeze.  The  average  yields  per  acre,  therefore,  were  much  smaller 
than  in  many  preceding  years,  although  the  total  crop  was  fairly  large. 

The  lemon  trees  wrere  much  more  severely  injured,  the  fruit- 
bearing  wood  being  destroyed  in  many  sections.  The  crop  of  the  year 
following  the  freeze,  1913-14,  was  thus  comparatively  small,  as  will 
be  seen  by  an  examination  of  table  4,  giving  the  yields  for  the  last 
nine  years. 

Planting  Frosted  Nursery  Trees. — During  the  summer  following 
the  freeze,  some  cases  were  reported  of  loss  due  to  the  planting  of 
nursery  trees  that  were  more  or  less  injured  by  the  freeze  in  January 
but  that  had  recovered  sufficiently  to  be  sold  for  planting  several 
months  later. 

The  reason  for  this  is  probably  due  to  the  fact  that  the  injured 
tree,  in  order  to  produce  a  new  top,  or  a  new  top  and  portion  of  the 
trunk,  must  draw  upon  its  reserve  food  material  stored  in  roots  and 
trunk  for  this  new  tissue,  and  that  the  trees  had  not  had  sufficient  time 
before  the  second  shock  of  transplanting  to  replenish  this  reduced 
reserve  food,  which  is  necessary  in  order  that  the  plant  may  recuperate 
when  set  in  the  orchard. 

Thawing  and  Recovery  of  Frozen  Fruit. — It  has  long  been  known 
that  if  frozen  tissue  is  suddenly  heated  or  thawed  rapidly,  it  is  severely 
injured,  but  if  gradually  thawed,  it  often  escapes  injury.  There 
seems  but  little  doubt  that,  had  the  freeze  of  1918  been  followed 
immediately  by  warm  sunny  weather,  instead  of  the  continued  cool, 
cloudy  weather  accompanied  by  light  showers,  that  devastation  would 
have  been  far  more  serious.  It  ma}'  be  stated,  however,  that  no  cases 
of  the  commercial  recovery  of  fruit  was  found.  Individual  fruits  have 
been  found  in  most  varieties  that  have  shown  a  development  of  new 
pulp  cells,  but  this  is  not  general  enough  to  be  of  commercial  impor- 
tance. Instead  of  recovering,  frozen  fruit  steadily  deteriorates. 

The  Sale  of  Frozen  Fruit. — A  large  proportion  of  the  crop  of 
citrus  fruits  was  badly  frozen,  but  in  many  cases  only  a  portion  of 
the  fruit  was  seriously  injured.  Frozen  fruit  is  known  to  remain 


296  UNIVERSITY  OP  CALIFORNIA — EXPERIMENT  STATION 

palatable  and  wholesome  for  a  month  or  two  after  a  freeze  if  properly 
handled.  Many  growers  immediately  gathered  and  shipped  large 
quantities  of  such  frozen  oranges,  but  in  many  cases  they  arrived  in 
poor  condition,  and  the  market  being  suspicious  and  overstocked, 
the  returns  were  in  most  cases  negligible.  Indeed  it  may  be  stated 
that  in  very  few,  if  any  cases  did  the  returns  justify  such  shipments, 
and  the  loss  to  the  growers  as  a  whole  through  the  injury  of  the 
market  was  far  greater  than  any  benefit  obtained.  The  shipment  of 
injured  fruit  was  continued  so  long  that  much  of  it  reached  the  con- 
sumers in  dried-out,  inedible  condition  and  served  to  render  them 
distrustful  of  the  California  product.  The  results  from  such  ship- 
ments following  the  1913  freeze  were  such  that  it  can  be  unhesitatingly 
recommended  that  in  the  case  of  such  severe  freezes,  no  shipments  of 
fruit  should  be  made  following  the  freeze,  until  sufficient  time  has 
elapsed  to  allow  the  separation  of  the  good  from  the  injured  fruit. 

It  was  thought  by  some  growers  that  oranges  picked  promptly 
after  the  freeze  and  stored  in  cool  places  or  placed  in  cold  storage, 
where  they  would  not  dry  out  too  rapidly  and  fermentation  would  be 
arrested,  would  remain  in  good  condition  for  a  much  longer  period 
than  otherwise.  No  trial  was  made  of  this  method  that  could  be  called 
complete  and  conclusive,  although  several  experiments  were  made.  In 
two  cases  one  of  the  writers  made  an  examination  of  navels  that  had 
been  picked  two  or  three  days  after  the  freeze  and  stored  in  a  cool 
place  in  the  packinghouse  (not  in  cold  storage).  This  examination 
was  made  in  March  over  two  months  after  the  freeze,  and  the  fruits 
were  compared  with  navels  from  the  same  groves  that  had  remained 
on  the  trees.  In  neither  case  could  any  marked  difference  be  observed 
between  the  stored  and  the  unstored  fruits.  In  both  cases  they  had 
dried  out  considerably,  and  the  flavor  had  become  flat  and  insipid. 

The  Separation  of  Good  Fruit  from  Frozen  Fruit. — In  many 
groves  all  over  the  state,  only  a  portion  of  the  fruit  was  so  severely 
frozen  as  to  cause  its  drying  out  and  decay.  The  good  fruit  in  most 
cases  was  mixed  on  the  tree  with  the  frozen  fruit  and  could  not  be 
separated  from  much  of  the  frozen  fruit  by  any  external  characters. 
The  making  of  a  practical  segregation  of  such  fruit  became  an  im- 
portant problem  following  the  1913  freeze,  as  it  had  been  also  in  many 
lesser  freezes.  No  method  of  separation  based  on  the  judgment  of 
external  appearances  proved  successful.  The  difference  in  specific 
gravity  between  frozen  and  sound  fruit  had  been  used  as  a  means  of 
making  a  segregation.  Finally,  as  a  result  of  drying  out  sufficient 
difference  in  specific  gravity  comes  to  exist  between  injured  and  unin- 
jured fruits,  so  that  a  solution  somewhat  lighter  than  water,  such 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  297 

as  denatured  alcohol,  guaged  to  the  right  specific  gravity,  will  allow 
the  heavy  uninjured  fruit  to  sink,  while  the  lighter  frozen  fruit  will 
float.  For  some  time  following  the  injury,  no  such  segregation  can 
be  made.  Time  must  be  given  for  the  changes  in  the  fruit  to  take  place. 
Lemons  change  more  rapidly  than  oranges,  and  give  a  fair  segregation 
within  a  mouth  following  the  freeze.  The  changes  are  much  slower 
in  oranges,  however,  and  it  was  about  two  months  after  the  freeze 
before  a  practical  segregation  by  this  method  could  be  obtained. 

A  machine  had  been  devised  to  make  this  specific  gravity  segrega- 
tion mechanically  in  alcohol,  and  had  the  previous  year  been  installed 
in  a  few  packing-houses.  This  machine  gave  fairly  good  results  as 
long  as  the  alcohol  remained  at  the  proper  degree  of  density.  Owing 
to  the  rapid  evaporation  of  the  alcohol  and  the  change  in  degree 
of  density,  considerable  difficulty  was  experienced  in  using  these 
machines. 

It  was  found  that  a  practical  and  fairly  economical  separation 
could  also  be  made  by  this  alcoholic  method,  using  special  tanks  or 
half  barrels,  into  which  open  mesh-bottomed  trays  were  fitted.  By  this 
method  the  tray  filled  with  fruit  was  dipped  into  the  alcohol.  The 
light  floating  oranges  could  then  be  removed  quickly  by  use  of  a  sieve 
dipper,  after  which  the  tray  could  be  lifted  out  and  the  heavy 
oranges  removed. 

In  certain  experiments,  oils,  such  as  kerosene  and  engine  distillate, 
have  been  used  instead  of  alcohol  in  making  specific  gravity  segre- 
gations, but  even  when  friuts  so  segregated  have  been  thoroughly 
washed  with  warm  water  and  "gold  dust"  to  remove  the  oils,  injury 
almost  always  ensues. 

The  alcoholic  method  of  segregation  was  the  only  successful 
method  known  during  the  first  two  months  following  the  freeze,  and 
many  were  preparing  to  use  it,  regardless  of  the  great  expense  for 
materials  and  the  difficulty  of  its  application.  Fortunately  just  at 
this  time,  before  much  expense  had  been  incurred  in  the  purchase  of 
alcohol  or  alcohol  separators,  Mr.  Frank  Chase  of  Riverside  rendered 
citrus  growers  a  great  and  lasting  service  by  patenting  a  water  sep- 
arator and  giving  the  patent  t«  them  for  use,  freely,  without  recom- 
pense, except  that  reward  of  personal  satisfaction  for  work  well  done 
and  the  honor  that  comes  to  one  from  the  performance  of  notable 
public  service. 

The  principle  of  the  Chase  water  separator  is  based  on  the  differ- 
ence in  the  specific  gravity  of  the  injured  and  uninjured  fruit  the 
same  as  in  the  case  of  the  alcoholic  separator.  In  the  Chase  separator, 
however,  the  fruits  are  carried  in  single  rows  and  dropped  from  a 


298  UNIVERSITY  OP  CALIFORNIA — EXPERIMENT  STATION 

slight  elevation,  about  six  inches,  into  a  current  of  water,  moving  at 
a  regular  speed.  The  injured,  light  oranges  do  not  sink  very  far  and 
come  up  quickly  so  that  they  are  only  carried  a  short  distance  before 
they  come  to  the  surface.  The  good  heavy  oranges  sink  much  deeper 
as  they  fall  and  come  to  the  surface  more  slowly  so  that  they  are 
carried  much  farther  by  the  current  of  water.  Taking  advantage  of 
this  principle,  a  screen,  placed  horizontally  at  a  certain  depth  in  the 
water  and  a  certain  distance  from  the  points  at  which  the  fruit  falls, 
will  allow  the  light,  frozen  oranges  to  arise  to  the  surface  and  be 
carried  off  above  the  screen;  while  the  heavy  oranges  will  not  arise 
until  they  pass  the  end  of  the  screen  and  thus  are  carried  on  below  it 
and  into  a  separate  receptacle,  or  passed  directly  into  the  washing 
machine  in  case  the  fruit  is  to  be  washed. 

Different  crops  of  fruit  have  different  specific  gravities,  or  the 
same  fruit  at  different  times  gives  a  different  specific  gravity,  so  that 
the  separating  screen  requires  to  be  adjusted  to  the  crop  that  is  being 
run  through  at  a  given  time.  When  it  is  properly  adjusted,  a  very 
satisfactory  segregation  can  be  made,  comparing  favorably  with  the 
best  alcoholic  segregation. 

The  practicality  of  this  method  of  segregation  was  immediately 
recognized,  and  separators  were  installed  in  the  various  packing- 
houses requiring  them,  as  rapidly  as  the  machines  could  be  con- 
structed. After  the  first  of  May,  practically  all  of  the  fruit  that  was 
shipped  from  the  state  was  run  through  Chase  separators  to  eliminate 
injured  fruit.  The  examination  of  such  separated  fruit,  and  the 
market  reports  from  the  separated  fruit  shipped,  testify  conclusively 
to  the  value  and  effectiveness  of  this  method  of  separation. 


BERKELEY,  CM.IFORM* 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  299 


CHANGES  THAT  TAKE  PLACE  IN  FROZEN  ORANGES  AND 

LEMONS* 
BY  E.  E.  THOMAS,  H.  D.  YOUNG,  AND  C.  O.  SMITH 

After  the  destruction  of  a  large  part  of  the  citrus  crop  by  the 
freeze  of  January  6th  and  7th,  1913,  it  was  thought  to  be  important 
to  make  some  studies  of  the  physical  and  chemical  changes  that  take 
place  in  frozen  oranges  and  lemons.  The  work  was  carried  out  at 
the  Citrus  Experiment  Station  and  was  intended  to  determine  as 
definitely  as  possible,  the  nature  and  rate  of  changes  that  take  place 
in  frozen  fruit.  While  it  is  not  impossible  that  the  composition  of 
the  ash  or  mineral  elements  may  be  affected,  it  was  not  considered 
advisable  to  attempt  to  determine  such  changes  in  the  time  at  the 
disposal  of  the  investigators  and  only  the  special  points  which  could 
most  reasonably  be  expected  to  show  variation  were  considered.  The 
following  points  were  taken  up  in  the  investigation : 

The  specific  gravity  of  the  fruits  and  of  the  juice. 

The  average  weight  per  fruit,  of  good  and  frozen  fruit. 

The  percentage  and  total  amount  of  sugar  (total  sugar,  sucrose 
and  reducing  sugars)  and  acid. 

Sound  fruit  and  badly  frozen  fruit  of  Washington  navel  oranges 
and  Eureka  lemons  were  picked  every  four  days  following  the  freeze 
for  two  and  one-half  months  and  these  were  weighed  and  analyzed. 
They  were  compared  with  sound  fruit  and  frozen  fruit  picked  imme- 
diately after  the  freeze  and  stored. 

Four  different  grades  of  fruit  were  examined. 

(a)  Fruit  known  to  be  unfrozen,  picked  from  trees  whose  blossoms 
and  small  fruits  showed  no  sign  of  frost  injury. 

(ft)  Fruit  which  was  apparently  unfrozen,  judging  from  external 
indications  and  picked  from  trees  slightly  injured  by  the  freeze. 

(c)  Fruit  supposedly  frozen,  picked  from  same  tree  as  sample  (6). 

(d)  Fruit  picked  from  badly  frozen  trees  about  which  there  could 
be  no  question  of  the  frost  injury. 

The  badly  frozen  lemons  were  picked  from  the  trees  shown  in  fig- 
ures 1  and  2.  Oranges  of  this  grade  were  obtained  from  large  navel 
trees  in  the  same  grove. 

*  A  summary  of  these  investigations  was  first  published  by  one  of  the  authors, 
H.  D.  Young,  while  he  was  employed  in  the  Citrus  Experiment  Station,  in  a  pape 
entitled  "The  Composition  of  Frozen  Oranges  and  Lemons."     See  Jour    ] 
Eng    Chem.,  vol.  7    p.  1038,  Dec.,  1915.     For  further  data  on  same  subject  see 
article  by  H.  S.  Bailey  and  C.  P.  Wilson,  "The  Composition  of  Sound  and  Frozen 
Lemons  with  Special  Reference  to  the  Effect  of  Slow  Thawing  on  Frozen  Lemons." 
Jour.  Ind.  and  Eng.  Chem.,  vol.  8,  p.  902,  Oct.,  1916.— H.  J.  Webber. 


300  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 


SPECIFIC  GEAVITY  OF  FEUITS 

The  work  done  in  previous  years  had  shown  that  the  specific 
gravity  of  frozen  fruit  decreases  and  that  the  frost  markings  on  the 
rind  are  unreliable  as  a  means  of  separation  (fig.  16).  It  was  found 
through  work  done  by  Mr.  D.  C.  Lefferts  of  Redlands,  California,  that 
frozen  fruit  was  usually  lighter  in  weight  than  sound  fruit  and  that 


Fig.  16. — Frozen  and  unfrozen  Eureka  lemons  showing  specific  gravity 
of  each  fruit.  The  fruit  with  a  specific  gravity  of  .81  is  free  from  frost 
markings  and  is  apparently  uninjured.  It  is,  however,  badly  frozen.  Photo 
by  Smith,  January  24,  1913. 

by  immersing  a  mixture  of  sound  and  frozen  fruit  in  a  suitable  liquid, 
such  as  alcohol,  the  two  classes  could  be  separated.  As  this  method 
of  procedure  proved  to  be  f airly  satisfactory,  a  machine  was  con- 
structed for  use  in  packing  houses  and  a  patent  granted  to  Mr.  D.  C. 
Lefferts  of  Redlands  and  to  Mr.  George  D.  Parker  of  Riverside,  cover- 
ing the  principle  involved.  Following  the  freeze  of  1913  another 
method  of  separation,  based  on  the  specific  gravity  of  frozen  and 
unfrozen  fruit  was  devised  by  Mr.  Frank  Chase  of  Riverside.  (See 
description,  page  297.) 

In  view  of  the  great  demand  for  exact  information  on  this  subject 
and  because  of  its  economic  importance,  a  statistical  study  was  made 
of  the  behavior  of  a  number  of  oranges  and  lemons  of  varying  degrees 
of  injury  by  the  frost. 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  301 

Definite  points  on  which  information  was  desired  were:  (1)  Do 
all  frozen  fruits  have  a  lower  specific  gravity  than  any  sound  fruit? 
(2)  If  so,  is  the  difference  great  enough  to  make  it  possible  to  separate 
the  two  classes  absolutely?  (3)  How  soon  after  the  freeze  is  it  possible 
to  detect  any  difference  that  may  occur?  (4)  What  changes  occur  in 
the  specific  gravity  of  the  fruit  if  it  is  picked  from  the  tree  and 
stored?  (5)  What  explanation  can  be  given  of  these  changes? 

The  specific  gravity  of  the  individual  fruits  was  found  by  dropping 
them  in  alcohol  of  varying  specific  gravity  until  that  of  the  fruit  and 
the  alcohol  was  the  same.  Jars  were  prepared  containing  alcohol  of 
specific  gravity  from  .82  to  .97  varying  from  each  other  by  .01.  The 
results  obtained  are  summarized  in  table  5.  For  the  sake  of  clearness 
only  the  figures  for  the  best  and  worst  fruit  are  presented.  The  inter- 
mediate classes  of  fruit  which  were  only  partially  frozen,  gave  results 
which  were  in  complete  agreement  with  those  presented. 

TABLETS. — Average  Specific  Gravity  of  Fruit. 


NAVEL  ORANGES 

ECREKA 

LEMONS 

Date 
1/14 
18 
22 
26 
30 
2/  3 
7 
11 
15 
19 
23 
27 
3/  3 
11 

(»)  Fruit 
(b)  Succ« 

Stored  lots  fa) 

Different  picks  (b) 

Stored  lots  (a) 

A 

Different  picks  (b) 

Unfrozen      Frozen 

0.876      0.850 
0.876      0.840 
0.884      0.838 
0.885      0.832 
0.884      0.821 
0.894      0.812 
0  903 

Unfrozen      Frozen 

0.876      0.850 
0.872      0.846 
0.874      0.834 
0.870      0.820 
0.864      0.810 

Unfrozen      Frozen 

0.890      0.860 
0.907      0.833 
0.926      0.807 
0.930      
0.941 
0.953       

Unfrozen 

0.890 
0.879 
0.889 
0.887 
0.869 

Frozen 

0.860 
0.834 
0.803 

0.873 

0.959 
0.966 

0.881 

0  914 

0  923 

0  880      

0.968      

.0873 

0  928 

0  936 

0  871 

0.863 

0  936 

0.869       

0.862 
0.865 

0  866 

picked  on  January  13th. 
•asive  new  lota  picked  on  date  given. 

The  first  two  columns  in  table  5  present  the  record  of  the  oranges 
picked  on  January  13  and  kept  in  storage,  the  specific  gravity  of  the 
fruit  being  determined  every  four  days.  The  average  specific  gravity 
of  the  stored  navel  oranges  which  were  unfrozen  incerased  from  .876 
on  the  date  of  picking,  to  .936  on  February  27.  The  average  specific 
gravity  of  the  badly  frozen  oranges  in  storage  decreased  from  .850 
on  the  date  of  picking  to  below  .820  on  February  3.*  The  third  and 

*  A  specific  gravity  of  .820  was  the  lowest  determined  with  the  jars  of  alcohol. 
Where  a  lower  specific  gravity  is  shown  in  the  tables  it  is  of  special  fruits. 


302  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

fourth  columns  give  the  specific  gravities  of  successive  new  lots  of 
oranges  picked  at  intervals  of  four  days.  The  specific  gravity  of  these 
unfrozen  oranges  does  not  change  appreciably,  varying  on  both  sides 
of  .876.  The  specific  gravity  of  the  badly  frozen  oranges  on  the  tree, 
however,  decreased  very  rapidly  from  .850  on  January  13  to  below 
.820  on  January  30.  Stored  lemons  show  the  same  changes  in  specific 
gravity  but  to  a  greater  degree  than  was  found  in  stored  navel 
oranges.  The  sound  lemons  increased  in  specific  gravity  from  .890  on 
January  14  to  .968  on  February  15,  while  the  badly  frozen  lemons 
decreased  from  .860  on  January  14  to  below  .820  on  January  22. 
We  also  find  that  the  fruits  picked  at  different  times  during  the 
experiment  (columns  7  and  8),  remain  practically  the  same  if  un- 
frozen, but  decreased  very  rapidly  in  specific  gravity  if  badly  frozen. 
We  thus  see  that  the  specific  gravity  of  the  fruit  which  is  frozen 
decreases  rapidly  whether  it  is  picked  and  stored  or  remains  on  the 
tree  and  that  the  fruit  which  is  unfrozen  increases  in  specific  gravity 
when  picked  from  the  tree  and  stored. 

Of  still  more  importance  than  the  average  specific  gravity  is  that 
of  the  specific  gravity  of  the  individual  fruit.  It  might  be  possible  for 
the  unfrozen  fruit  to  have  a  much  higher  average  than  the  frozen  and 
yet  the  specific  gravity  be  so  variable  among  the  individuals  as  to 
make  a  separation  impossible.  This  is  the  condition  for  some  time 
after  the  freeze.  In  table  6  is  shown  the  records  of  individuals.  The 
number  of  fruit  of  each  density  on  the  date  of  picking  is  shown  and 
the  number  in  the  same  lot  of  fruit  two  weeks  later.  The  fruit  was 

TABLE  6. — Number  of  Navel  Oranges  Picked  on  January  13,  1913  which  had  a  Specific 
Gravity  of  Above  or  Below  .87,  and  their  Subsequent  Changes. 

Unfrozen  Frozen 


.87  or 
above 

below 

.87 

.87  or 
above 

below 

.87 

29 

26 

7 

25 

41 

14 

6 

26 

55 

0 

6 

26 

Jan.  14,  1913 

Jan.  26,  1913 41 

Feb.  15,  1913 55 

Number  of  Eureka  Lemons  Picked  on  January  13,  With  a  Specific  Gravity  of  Above  or 
Below  .  89,  and  their  Subsequent  Changes. 

Unfrozen  Frozen 


.  89  or  below  .  89  or  below 

above  .89  above       .89 

Jan.  13,  1913 61  3  12        32 

Jan.  26,  1913 64  0  2        42 

Feb.  15,  1913 64  0  1        43 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA 


303 


304  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

classed  "unfrozen"  and  "frozen"  according  to  its  appearance  on 
being  cut. 

In  the  fruit  picked  on  January  13,  of  the  fifty-five  sound  oranges, 
twenty-nine  had  a  specific  gravity  of  .87  or  more.  Of  the  thirty-two 
frozen  ones,  seven  were  also  .87  or  more.  If,  therefore,  an  attempt 
had  been  made  to  separate  the  sound  from  the  frozen  using  .87  as  the 
point  of  separation,  twenty-six  good  fruits  would  have  gone  out  with 
the  injured  ones  and  seven  frozen  ones  would  have  been  retained. 
Two  weeks  later,  however,  a  similar  separation  would  have  recovered 
forty-one  good  oranges  and  six  frozen  ones.  At  the  end  of  a  month, 
all  of  the  sound  oranges  had  a  specific  gravity  of  .87  or  above,  while 
all  but  six  of  the  frozen  fruit  were  below  this  point.  The  effectiveness 
of  holding  oranges  two  weeks  or  a  month  after  picking,  before  separa- 
tion, is,  therefore,  very  clearly  demonstrated. 

Subsequent  picks  illustrate  the  same  principle.  The  most  favor- 
able points  of  separation  are  not  constant  throughout,  however,  nor 
is  the  percentage  of  recovery  absolutely  uniform.  In  the  fruit  picked 
on  January  18  the  separation  of  the  oranges  would  have  been  made  at 
.88  two  weeks  after  picking,  to  eliminate  all  frozen  fruit,  and  thus 
five  sound  ones  would  have  been  lost.  In  fruit  picked  on  January  22 
the  same  point,  .88,  would  have  eliminated  all  frozen  oranges,  but  it 
would  also  have  thrown  out  twenty-five  out  of  forty-two  good  ones. 
Even  a  separation  at  .84  would  have  lost  five  good  ones,  while  includ- 
ing fourteen  frozen  ones.  In  such  fruit  a  single  separation  becomes 
inefficient.  By  making  three  grades,  one  below  .83,  the  other  between 
.83  and  .87,  and  the  third  above  .87,  very  satisfactory  results  could 
have  been  obtained.  By  January  25  the  frozen  fruit  on  the  trees  had 
so  decreased  in  specific  gravity  that  it  was  possible  to  eliminate  it 
quite  completely.  Even  at  this  date,  however,  it  was  not  possible  to 
prevent  some  loss  of  good  fruit  unless  the  fruit  was  kept  in  storage 
for  some  time  before  the  separation  was  made.  In  fruit  picked  on 
January  25,  sixteen  of  the  forty-two  good  oranges  were  .84  or  below, 
while  there  were  three  frozen  ones  above  that  figure.  Two  weeks  later 
there  were  still  seven  good  oranges  below  .84  and  five  frozen  ones 
above  that  point. 

The  lemons  show  a  much  sharper  line  of  demarcation.  On  the 
date  of  picking,  January  13,  three  of  the  sixty-four  good  lemons  were 
below  .89  in  specific  gravity  and  twelve  of  the  forty-four  frozen  ones 
were  .89  or  above.  Two  weeks  later  all  of  the  good  lemons  had  a 
specific  gravity  of  .89  or  above  and  all  but  two  frozen  fruits  (one  of 
which  is  shown  in,  figure  17)  were  below  that  mark,  so  that  a  very 
complete  separation  could  have  been  effected. 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA 


305 


Photo  by  Smith,  March  28,  1913 


306  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

In  different  sections  the  specific  gravity  of  the  good  fruit  may  be 
higher  or  lower  than  that  found  in  the  experiments  here  recorded,  but 
the  general  conclusion  will  be  the  same  in  the  various  districts,  namely, 
that  the  specific  gravity  of  good  fruit  will  increase  in  storage  and  that 
of  frozen  fruit  will  decrease. 

The  explanation  of  the  change  in  specific  gravity  of  sound  and 
frozen  fruit  seems  to  be  as  follows:  Freezing  kills  the  walls  of  the 
cells  in  the  fruit  and  so  changes  it  from  a  living,  semi-permeable 
membrane  to  a  dead,  porous  mass,  acting  like  a  sponge.  In  the  frozen 
fruit,  therefore,  connection  is  established  between  the  rind  and  the 
pulp  and  the  water  which  is  evaporated  from  the  outside  of  the  rind 
is  supplied  from  the  pulp  without  the  fruit  suffering  much  diminution 
of  volume.  Losing  weight  and  retaining  approximately  its  original 
volume,  it  must,  obviously,  decrease  in  specific  gravity.  The  unfrozen 
fruit  on  the  other  hand,  loses  very  little,  if  any,  moisture,  except  from 
the  rind.  This  shrinks  down  very  markedly  and  so  decreases  the 
volume  of  the  fruit.  As  the  weight  does  not  decrease  proportionately, 
the  specific  gravity  increases.  The  difference  in  the  evaporation  from 
the  rind  is  shown  very  clearly  in  figure  18.  These  two  oranges  were 
picked  on  January  13  and  stored  for  two  months.  They  were  the 
same  size,  3%  e  inches  in  diameter,  on  picking.  When  they  were  cut 
the  sound  fruit  had  decreased  to  2%  inches  while  the  frozen  one  had 
lost  only  %6  inch,  measuring  3  inches  in  diameter. 

SPECIFIC  GKAVITY  OF  JUICE 

It  was  not  possible  to  make  a  determination  of  the  specific  gravity 
of  the  juice  on  all  of  the  samples  used  on  account  of  their  large  num- 
ber; therefore,  the  data  which  is  presented  in  table  3  shows  a  rather 
irregular  appearance.  The  specific  gravity  of  the  juice  of  unfrozen 
oranges  in  storage  does  not  seem  to  change  appreciably  but  it  remains 
consistently  greater  than  that  of  the  frozen  oranges.  The  juice  of  the 
frozen  oranges  in  storage  had  an  average  specific  gravity  of  1.046 
throughout  a  greater  part  of  the  experiment  and  increased  quite 
markedly  toward  its  expiration.  The  juice  of  the  sound  oranges  had 
an  average  of  1.052  which  remained  approximately  constant.  The 
specific  gravity  of  the  juice  of  frozen  oranges  picked  at  different 
intervals  did  not  increase,  as  with  frozen  oranges  in  storage,  but 
remained  constant  (see  table  7). 

The  average  specific  gravity  of  the  juice  of  the  lemons  showed 
about  the  same  differences.  The  juice  of  the  sound  fruit  had  a  higher 
specific  gravity  than  that  of  the  frozen.  There  are  more  irregularities 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA 


307 


in  the  tables  for  lemons,  due  to  the  difficulty  in  getting  samples  of 
uniform  ripeness.  By  January  30  the  frozen  lemons  in  storage  had 
dried  out  so  completely  that  it  was  no  longer  possible  to  get  enough 
juice  to  determine  the  specific  gravity.  At  this  time  twenty  lemons 
which  were  picked  on  January  13  yielded  a  total  of  only  thirty-one 
cubic  centimeters  of  juice. 

TABLE  7. — Average  Specific  Gravity  of  Juice. 


NAVEL  ORANGES 


EUREKA  LEMONS 


Stored  lots  (a) 

Different  picks  (o) 

Stored  lots  (a) 

Different  picks  (hi 

Date 

Unfrozen 

Frozen 

Unfrozen 

Frozen 

Unfrozen 

Frozen 

Unfrozen 

Frozen 

1/14 

1  053 

1   053 

1   060 

1.060 

18 

1.052 

1.042 

1.052 

1.044 

1.042 

1.042 

1.048 

1.046 

22 

1.055 

1.044 

1.056 

1.046 

1.050 

1.041 

1.053 

1.046 

26 

1.047 

1.046 

1.055 

1.047 

1.045 

1.040 

1.044 

1.041 

30 

1.050 

1.045 

1.045 

1.040 

1.046 

1.038 

1.046 

1.037 

2/  3 

1  051 

1  045 

1  043 

1.046 

1.040 

7 

1  056 

1  045 

1  045 

1.050 

1.045 

1.038 

1  053 

1  044 

1  050 

1  048 

1  044 

15 

1  053 

1.048 

1.052 

1.042 

1.038 

19 

1  048 

1  050 

1.051 

1.042 

1.038 

23 

1  056 

1  042 

27 

1  055 

1  054 

3/  3 

11  Av. 

1.052 

1.046 

1.051 

1.045 

1.049 

1.040 

1.046 

1.040 

(a)  Fruit  picked  on  January  13th. 

(b)  Successive  new  lots  picked  on  date  given. 


TABLE  8.— Per  Cent  Total  Sugar  in  Juice* 


N  SVEL  ORANGES 


Date 
1/14 

18 

22 

26 

30 
2/  7 

15 

23 

3/  3 
7 

15 
Average 

(a)  Fruit  picked  on  January  13th. 

(b)  Successive  new  lots  picked  on  date  given. 

*  The  sugars  were  determined  by  Bertrand'a  method. 


EUREKA  LEMONS 


Stored  lots  (a) 

Different  picks  (b) 

Stored  lots  (a) 

Different  picks  (b) 

Unfrozen 

Frozen 

Unfrozen 

Frozen 

Unfrozen 

Frozen 

Unfrozen 

Frozen 

10  56 

10   56 

3.39 

3.39 

9.18 

6.54 

8.92 

7.86 

2.85 

2.47 

2.64 

3.16 

8.87 

7.08 

9.43 

7.51 

2.88 

2.12 

3.12 

2.89 

8.07 

7.28 

9.39 

7.44 

2.07 

2.41 

2.94 

2.47 

8.32 

7.29 

7.50 

6.38 

2.83 

2.33 

3.67 

2.95 

9  11 

8.09 

6.99 

2.71 

3.14 

2.57 

1.60 

Q   fi7 

7  85 

7  01 

2  69 

2.77 

2.24 

Q   17 

7  17 

9  00 

8  03 

2.96 

2.54 

10  11 

8.82 

2.79 

2.57 

2.11 

Q  28 

7  96 

9  41 

6.94 

3.30 

2.21 

842 

8  63 

2  97 

9.06 

7.42 

9.03 

7.44 

2.79 

2.49 

2.99 

2.46 

DIVISION  OF  SUblROPm  HOMICUUUPE 
COLLEGE  OF  AGRICULTURE 


308  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 


SUGAR  CONTENTS 

The  unfrozen  oranges  in  storage  show  a  variation  in  the  amount 
of  sugar  present,  but  show  no  progressive  changes,  thus  indicating 
that  the  variation  is  probably  due  to  the  difference  in  individual 
samples  taken  for  analysis.  The  average  of  the  unfrozen  lots  in 
storage  was  9.06  per  cent  and  the  frozen  7.42  per  cent  throughout 
the  experiment.  The  average  percentage  of  sugar  for  the  fruit  picked 
at  different  dates  was  very  close  to  that  of  the  stored  fruits,  the 
difference  being  within  the  limits  of  experimental  error.  The  per- 
centage of  sugar  in  the  juice  of  the  lemons  shows  the  same  kind  of 
variation  as  was  the  case  with  the  oranges  (see  table  8). 

The  great  change  which  has  been  taking  place  in  the  fruit  is  more 
clearly  illustrated  when  we  consider  the  actual  amount  of  sugar  present 
in  the  individual  fruits  (table  9).  While  the  figures  for  the  total 

TABLE  9. — Grams  of  Sugar  per  Fruit. 

NAVEL  ORANGES  EUREKA  LEMONS 


Stored  lots  (a) 

A 

Different  picks  (b) 

Date 

Unfrozen 

Frozen 

Unfrozen 

Frozen 

1/14 

7.2 

7.2 

18 

5.3 

3.6 

5.0 

4.3 

22 

7.9 

3.4 

6.6 

3.6 

26 

4.9 

2.2 

7.3 

3.2 

30 

6.2 

2.9 

6.4 

3.8 

2/  7 

5.8 

5.8 

2.3 

15 

7.9 

6.3 

2.3 

23 

7.6 

3.1 

8.8 

2.0 

3/  3 

8.0 

2.1 

7 

7.0 

1.9 

11 

8.5 

1.9 

15 

fi.1 

1.8 

(a)  Fruit  picked  on  January  13th. 

(b)  Successive  new  lots  picked  on  date  given. 

Stored  lots  (a)  Different  picks  (b) 


Unfrozen      Frozen         Unfrozen  Frozen 

1.3          1.3 

1.0          0.7  0.8  0.9 

1.2          0.4  1.1  0.5 

0.8          0.3  1.2  0.4 

1.0          0.2  1.3  0.3 

1.0          0.2  0.9  0.1 

0.8          1.0  0.08 

1.2  0.08 

1.0  1.2  0.2 

0.9  0.08 

0.9 


amount  of  sugar  given  in  grams  per  fruit  is  admittedly  not  exact, 
because  of  the  difficulty  of  extracting  all  of  the  juice,  yet,  in  view  of 
the  fact  that  the  same  size  oranges,  150's,  and  lemons  of  standard  ring 
size  were  used  in  all  cases,  it  permits  a  basis  of  comparison  that  is 
more  striking  than  the  percentage  composition.  It  is  more  important 
to  know,  for  example,  that  on  February  23rd  the  sound  orange  con- 
tained 8.8  grams  of  sugar,  while  the  frozen  one  contained  2  grams, 
than  it  is  that  the  percentage  of  sugar  in  the  first  lot  was  9  per  cent 
and  in  the  second  was  8.03  per  cent.  When  we  consider  the  average 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA 


309 


amount  of  sugar  in  grams  per  fruit,  we  find  that  in  badly  frozen 
oranges  in  storage  it  drops  to  less  than  2  grams  per  fruit  against  an 
average  of  6.5  grams  for  an  unfrozen  fruit.  The  fruit  remaining  on 
the  tree  showed  almost  the  same  difference,  the  frozen  fruit  dropping 
to  the  same  point,  while  the  good  fruit  showed  a  slightly  greater 
average  than  the  stored  fruit,  or  6.9  grams.  The  lemons  again  showed 
the  same  kind  of  variation  as  is  found  in  the  oranges,  but  in  a  different 


TABLE  10. — Per  Cent  Invert 

NAVEL  ORANGES 


Sugar  in  Juice. 

EUREKA  LEMONS 


Stored  lots  X») 

Different  picks  (b) 

Stored  lots  (a) 

Different  picks  (b) 

Date 

Unfrozen 

Frozen 

Unfrozen 

Frozen 

Unfrozen 

Frozen 

Unfrozen 

Frozen 

1/14 
18 

4.69 
4.10 

4.69 
4.13 

3.75 

2.36 

2.11 

2.36 
2.26 

3.39 

1.53 

2.03 

22 

4.33 

3.60 

4.17 

3.76 

2.24 

1.55 

2.09 

1.85 

26 

4.06 

3.76 

4.70 

3.88 

1.74 

1.56 

2.30 

1.57 

30 

4.35 

3.60 

3.66 

3.37 

1.91 

1.48 

2.46 

1.89 

2/  7 

4  60 

3.49 

3.57 

2.26 

2.09 

1.98 

1.30 

1  K 

51ft 

3  48 

3  73 

2.22 

.    2.35 

1.73 

3CC 

4  no 

3  71 

2.30 

1.79 

23 
3/  3 

.00 

4.77 

3.85 

2.25 

1.42 

1.99 

1.50 

_   „_ 

.  lo 

' 

4  11 

3.45 

2.66 

1.74 

2  42 

15 
Average 

.0? 
4.62 

3.60 

4.12 

3.67 

2.16 

1.60 

2.27 

1.71 

(a)  Fruit  picked  on  January  13th. 

(b)  Successive  new  lots  picked  on  date  given. 

TABLE  11. — Per  Cent  Sucrose  in  Juice. 


NAVEL  ORANGES 

EUREKA  LEMONS 

Stored  lots  (a) 

Different  picks  (b) 

Stored  lots  (a) 

A 

Different  picks  (b) 

Date 

Unfrozen 

Frozen 

Unfrozen 

Frozen 

Unfrozen 

Frozen 

Unfrozen 

Frozen 

1/14 
18 

5.87 
5.08 

3.15 

5.87 
4.79 

4.11 

1.03 
0.74 

0.94 

1.03 

0.38 

1.13 

22 
26 

4.54 
4.01 

3.48 
3.52 

5.26 
4.69 

3.75 
3.76 

0.62 
0.33 

0.50 
0.85 

1.03 
0.64 

1.04 
0.90 

30 

3.97 

3.69 

3.84 

3.01 

0.92 

0.85 

1.21 

1.06 

2/  7 
15 

4.51 
4  51 

4.60 
4.37 

3.42 
3.28 

0.45 
0.43 

1.05 

0.59 
0.42 

0.30 
0.51 

23 

3/  3 

4.29 

3.61 

5.00 
5.34 

4.32 
4.97 

0.66 
0.58 

0.75 
0.61 

0.54 

, 

7 

.  10 

5  30 

3.49 

0.64 

0.47 

0  55 

15 
Average 

3.55 
4.44 

.00 
3.82 

4.90 

3.79 

0.62 

0.84 

0.72 

0  75 

(a)  Fruit  picked  on  January  13th. 

(b)  Successive  new  lots  picked  on  date  given. 


310  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

degree.  The  unfrozen  lemons  held  in  storage  averaged  1  gram  of 
sugar  per  fruit,  while  those  that  were  frozen  decreased  from  .7  to  .2 
gram  per  fruit.  The  fruit  which  remained  on  the  tree  showed  about 
the  same  amount  of  variation. 

The  tables  for  invert  sugar  and  sucrose  present  data  that  is  little 
different  from  those  in  the  total  sugar  (see  tables  10  and  11).  In 
other  words,  there  seems  to  be  practically  no  change  in  the  relative 
amounts  of  the  different  classes  of  sugar  present. 

ACID  CONTENTS 

The  percentage  of  acid  in  the  frozen  and  unfrozen  oranges  in 
storage  decreased  in  almost  the  same  degree.  The  fruit  picked  at 
different  intervals  showed  the  same  change  in  acidity  as  the  fruit  in 
storage,  but  had  a  lower  average.  Owing  to  the  fact  that  lemons 
have  a  much  higher  percentage  of  acid  than  do  the  oranges,  a  much 
greater  variation  is  found  between  the  unfrozen  and  frozen  fruit. 
The  unfrozen  lemons  kept  in  storage  averaged  6.98  per  cent  acid 
throughout  the  experiment,  while  the  frozen  ones  averaged  5.19  per 
cent.  The  acid  in  the  fruit  picked  at  different  intervals  averaged 
6.27  per  cent  in  unfrozen  lemons  and  4.79  per  cent  in  frozen  samples 
(see  table  12). 

r  FE  TABLE  12. — Per  Cent  Acid  in  Juice* 


Date 
1/14 

18 

22 

26 

30 
2/  7 

15 

23 

3/  3 

7 

11 

15 
Average 

(a)  Fruit  picked  on  January  13th. 

(b)  Successive  new  lots  picked  on  date  given. 

*  The  acid  was  determined  by  titration,  usins;  phenolphthalein  as  an  indicator  and  was  calculated  to 
anhydrous  citric  acid. 

We  find  again,  however,  that,  as  with  sugar,  the  total  amount 
of  acid  present  decreases  very  markedly  in  the  frozen  fruit.     The 


NAVEL  ORANGES 

EUREKA 

LEMONS 

Stored  lots  (a) 

A 

Different  picks  (b) 

A 

Stored  lots  (a) 

A 

Different  picks  (b) 

A 

Unfrozen 

Frozen 

Unfrozen 

Frozen 

Unfrozen 

Frozen 

Unfrozen 

Frozen 

1.56 

1.56 

5.81 

5.81 

1.56 

1.60 

1.45 

1.38 

5.70 

5.01 

6.64 

4.23 

1.67 

1.62 

1.68 

1.49 

6.96 

5.34 

7.23 

5.02 

1.47 

1.74 

1.69 

1.83 

7.54 

4.74 

4.67 

1.68 

1.88 

1.53 

1.59 

7.67 

4.98 

6.49 

3.66 

1.68 

1.50 

1.51 

7.00 

5.26 

6.53 

4.72 

1.59 

1.31 

1.34 

6.72 

6.32 

5.18 

1  40 

1  29 

1  22 

1.37 

5.64 

4.72 

1.38 

1.15 

7.76 

5.79 

6.19 

5.73 

1  19 

1  14 

1  20 

1.21 

5.23 

1  11 

1  20 

7.73 

5.65 

1.49 

1.49 

1.45 

1.43 

6.98 

5.19 

6.27 

4.79 

EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  31 1 

frozen  oranges  showed  .3  of  a  gram  of  acid  per  fruit,  in  comparison 
with  an  average  of  about  1  gram  per  fruit  in  unfrozen  oranges.  The 
unfrozen  lemons  vary  to  a  considerable  degree  in  the  amount  of  acids 
present,  ranging  from  2  to  3  grams  per  fruit,  while  in  the  frozen  fruit 
it  practically  all  disappears  (see  table  13). 

TABLE  13. — Grams  Acid  Per  Fruit. 

NAVEL  ORANGES  EUREKA  LEMONS 


Stored  lota  (a)  Different  picks  (b)  Stored  lots  (a)  Different  picks  (b) 


Date 

Unfrozen 

Frozen 

Unfrozen 

Frozen 

Unfrozen 

Frozen 

Unfrozen 

Frozen 

1/14 

1.1 

1.1 

2.3 

2.3 

18 

0.9 

0.9 

0.8 

0.8 

2.0 

1.5 

2.0 

1.2 

22 

1.3 

0.8 

1.2 

0.7 

2.9 

1.0 

2.4 

0.8 

26 

0.9 

0.5 

1.3 

0.8 

2.9 

0.7 

0.7 

30 

1.2 

0.7 

1.3 

0.9 

2.8 

0.4 

2.3 

0.4 

2/  7 

1.1 

1.1 

0.5 

2.7 

0.3 

2.2 

0.3 

15 

1.3 

1.0 

0.4 

2.0 

2.3 

0.2 

23 

1.2 

0.6 

1.2 

0.3 

2.3 

0.2 

3/  3 

1.1 

0.3 

2.8 

0.1 

3.0 

0.5 

7 

0.9 

0.3 

1.6 

0.2 

11 

1.1 

0.3 

15 

0.7 

0.3 

2.4 

(a)  Fruit  picked  on  January  13th. 

(b)  Successive  new  lots  picked  on  date  izrfven. 

Following  any  severe  freeze  growers  are  confronted  with  the  prob- 
lem of  whether  injured  fruit  should  be  harvested  immediately  and 
used  for  by-products  or  whether  the  picking  should  be  delayed  until 
the  extent  of  the  injury  becomes  apparent.  The  rapid  decrease  that 
takes  place  in  the  amount  of  sugar  and  acid  per  fruit  in  both  oranges 
and  lemons  as  shown  by  the  above  tables,  indicates  that  frozen  fruit, 
if  it  is  to  be  used  for  by-products  should  be  picked  and  sold  as  soon 
after  the  freeze  as  possible. 

GROWTH  OF  FROZEN  FRUIT 

When  fruit  is  badly  frozen  the  question  arises  whether  the  tree 
would  be  harmed  should  the  fruit  remain  upon  the  branches  until  it 
falls  naturally.  If  the  frozen  fruit  did  not  grow,  but  remained  on 
the  tree  in  the  same  condition  as  when  frozen,  it  would  presumably 
take  little  nourishment  from  the  tree  with  the  exception  of  the  mois- 
ture evaportaed  from  the  rind.  In  order  to  determine  this  point, 
several  hundred  Valencia  oranges  were  marked  and  measured  and 
their  growth  was  noted  each  month  for  four  months.  Groves  for  this 


IA*S»ON  OF  SUBTROPICAL  HORTICULTURE 
COLLEGE  OF  AGRICULTURE 
BERKELEY.  C 


312  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

work  were  chosen  where  part  of  the  fruit  was  frozen  while  the  re- 
mainder was  untouched  by  the  freeze.  Different  types  of  fruit  were 
marked  and  only  those  with  an  apparently  uninjured  stem  were 
selected  for  the  experiment.  In  one  class  the  fruit  was  green  and 
normally  would  have  increased  in  size.  In  another  class  the  fruit 
was  yellow  and  almost  ripe  and  would  not  increase  in  size  like  the 
green  fruit.  In  measuring  the  fruit  the  circumference  was  measured 
in  inches.  The  same  observations  were  carried  on  in  regard  to  the 
growth  of  frozen  lemons,  and  the  results  are  given  in  the  following 
table : 

TABLE   14.— AVERAGE  INCREASE   IN   CIRCUMFERENCE   OF   FROZEN   AND   UNFROZEN 
VALENCIAS  AND  LEMONS  FROM  JANUARY  24  TO  JUNE  2,  1913 

Good  fruit, 

full  of  juice  Fruit  Fruit 

and  good  slightly  badly 

flavor  frozen  frozen 

inches  inches  inches 

Valencia,    yellow    fruit   which    was    very 

nearly  ripe  at  the  time  of  the  freeze 58  49 

Valencia,  fruit  green;  thrifty  groves  not 

badly  frozen  71  .56 

Valencia,  fruit  green;  grove  badly  frozen       .48  .34 

Valencia,    fruit    almost    ripe    and    badly 

frozen  --  -33  .10 

Eureka  lemons — one-half  of  the  fruit  on 

the  trees  frozen 71  .54  .32 

From  this  table  we  see  that  the  fruits  have  grown  in  circumference. 
In  a  few  instances,  however,  the  stem  was  found  to  be  injured  and 
the  fruit  gradually  decreased  in  size.  The  juice  had  almost  disap- 
peared in  the  badly  frozen  fruit,  leaving  it  hollow.  In  the  good  fruit 
the  increase  in  circumference  is  approximately  twice  that  of  the  badly 
frozen  fruit.  The  rind  of  frozen  fruits  increases  in  thickness  (fig.  19), 
thus  probably  taking  nourishment,  or  at  least  water,  from  the  tree.* 


SUMMARY 

1.  The  specific  gravity  of  frozen  citrus  fruits,  in  general,  is  lower 
than  that  of  unfrozen  ones.    This  is,  however,  not  an  absolute  rule. 

2.  The  two  classes  cannot  be  absolutely  separated,  but  the  division 
is  sufficiently  complete  to  make  it  commercially  practical.     Different 

*  Note. — Observations  on  various  groves  in  the  state  lead  the  authors  of  the 
first  article  in  this  bulletin  to  conclude  that  no  noticeable  effect  was  produced  by 
leaving  the  frozen  fruits  on  the  tree.  Compare  page  289.  That  the  fruit  when  not 
too  badly  frozen  increases  in  size  the  authors  of  this  paper  have  proven.  Such 
fruit,  however,  evidently  losses  in  weight. — H.  J.  Webber. 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA 


313 


machines  have  been  ^perfected  and  are  used  in  packing  houses  to  make 
this  separation. 

3.  Severely  frozen  fruit  will  usually  show  a  marked  decrease  in 
specific  gravity  within  a  week;  less  severely  injured  fruit  changes 
more  slowly.    In  lemons  the  changes  in  specific  gravity  are  more  rapid 
than  in  oranges. 

4.  Holding  the  fruit  for  two  weeks  after  picking  increases  the 
specific  gravity  of  good  fruit  very  markedly.    A  month  is  generally 
long  enough  to  make  a  recognizable  difference,  but  better  separations 
can  be  obtained  after  six  weeks  or  two  months. 


Fig.  19. — Badly  frozen  orange  showing  growth  of  rind  when  fruit  remains 
on  tree.     Photo  by  Smith,  March  7,  1913. 

5.  Frozen  fruit  decreases  in  specific  gravity  whether  stored  or  left 
on  the  tree.     Sound  fruit,  however,  remains  fairly  constant  on  the 
trees,  but  gradually  increases  in  density  when  stored. 

6.  The  excessive  loss  of  moisture  in  citrus  fruits  caused  by  freezing 
is  due  to  the  killing  of  the  walls  of  the  cells  in  the  fruit,  thus  changing 
them  form   semi-permeable  membranes  to  a   porous  substance   that 
freely  allows  the  liquid  to  evaporate  from  the  interior  without  de- 
creasing its  volume.    This  loss  in  weight  and  not  in  volume  decreases 
the  specific  gravity. 

7.  The  specific  gravity  of  the  juice  of  frozen  citrus  fruit  is  some- 
what lower  than  that  of  the  unfrozen. 


314  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

8.  The  total  amount  of  sugars  decreases  in  frozen  fruit.     The 
average  amount  in  unfrozen  oranges  of  size  150  's  being  6.5  grams, 
while  in  those  that  are  frozen  it  decreases  to  less  than  2  grams.    The 
same  holds  true  with  lemons.    Unfrozen  lemons  of  standard  ring  size 
have  an  average  of  1  gram  per  fruit,  while  those  that  are  frozen 
decrease  from  .7  to  .2  gram  per  fruit. 

9.  No  change  was  found  in  the  relative  amounts  of  the  different 
sugars  present. 

10.  The  per  cent  of  acid  in  the  juice  of  frozen  citrus  fruits  de- 
creases slightly  when  compared  with  the  unfrozen.     The  weight  of 
acid  per  fruit  in  unfrozen  fruit  remains  nearly  constant,  while  in 
that  which  is  frozen  it  continues  to  decrease  until  practically  none 
remains. 

11.  Frosted  citrus  fruits  that  remain  on  the  tree  continue  to  in- 
crease in  size,  this  development  being  a  thickening  of  the  rind. 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  315 

A  TEST  OF  THE  EFFICIENCY  OF  ORCHARD  HEATING 

BY  A.  D.  8HAMEL,  L.  B.  SCOTT,  AND  C.  S.  POMEROY 

United  States  Department  of  Agriculture 

The  serious  damage  done  by  the  freeze  of  1913  awakened  a  general 
interest  in  ways  and  means  for  protecting  citrus  orchards  from  this 
danger.  In  many  sections  various  means  of  protection  were  in  use 
during  the  freeze,  but  exact  figures  were  lacking  in  many  cases  as  to 
the  profitableness  of  the  heating  methods  used. 

The  opportunity  of  securing  some  practical  information  in  an 
experimental  way  on  the  results  that  had  been  obtained  seemed  too 
good  to  lose.  Consequently  the  writers  in  co-operation  with  Dr.  H.  J. 
Webber  of  the  Citrus  Experiment  Station  of  the  University  of  Cali- 
fornia decided  to  secure  data  on  this  subject  in  connection  with  their 
citrus  performance-record  work  for  the  improvement  of  citrus  fruits 
by  bud  selection. 

After  consultation  it  was  decided  to  confine  observations  to  lemon 
varieties  and  to  orchards  located  in  the  Corona  district.  In  this 
district  an  unusual  number  of  groves  were  protected  by  heaters  during 
the  freeze,  and  in  many  cases  unprotected  orchards  adjoined  the  pro- 
tected ones. 

Shortlj*  after  the  freeze,  a  committee  of  Corona  lemon  growers, 
Dr.  H.  J.  Webber,  and  the  writers  visited  most  of  the  lemon  groves 
in  the  Corona  district  for  the  purpose  of  determining  whether  or  not 
reliable  data  on  the  efficiency  of  the  methods  of  orchard  protection 
could  be  obtained.  After  a  careful  survey  of  the  situation,  it  was 
unanimously  decided  that  such  information  could  be  secured  under 
fair  and  comparable  conditions.  Therefore,  several  orchards  were 
selected  for  study  and  observation  that  in  the  opinion  of  every  one 
in  the  party  were  suitable  for  this  purpose. 

The  plan  of  study  agreed  upon  was  to  keep  performance-records 
of  comparable  plots  of  trees  in  heated  and  unheated  groves,  beginning 
with  the  first  pick  after  the  frost  and  continuing  for  at  least-  one  year, 
and  if  advisable  for  a  longer  period  of  time. 

It  was  soon  apparent  that  lemon  varieties  differ  in  their  resistance 
to  frost.  So  it  became  necessary  to  compare  heated  and  unheated 
orchards  of  the  same  variety.  Not  only  was  this  difference  very 
evident,  but  different  types  in  the  same  variety  apparently  differ  in 
resistance  to  frost,  so  that  it  became  necessary  to  compare  trees  of  the 
same  type  in  heated  and  unheated  groves. 


316  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


Fig   20  — The  effect  of  the  freeze  on  unheated  Lisbon  lemon  tree.     Compare 

fig.  21. 

In  view  of  the  great  amount  of  detailed  record-keeping  involved 
for  each  individual  tree,  it  was  found  necessary  to  limit  the  number 
of  trees  for  observation.  In  order  to  combine  reliability  of  data  and 
limit  the  number  of  trees  to  the  smallest  possible  number,  the  fol- 
lowing plan  of  plot  arrangement  was  carried  out.  First,  comparable 
orchards  were  selected.  Then  a  plot  of  ten  trees  in  each  orchard  was 
arranged  on  the  following  basis:  Two  adjoining  trees  were  marked 
for  observation.  Counting  these  trees  as  numbers  1  and  ^2,  respec- 
tively, the  ninth  and  tenth  trees  in  the  same  row  were  also  marked. 
Corresponding  trees,  ten  rows  from  this  row,  were  then  marked,  so 
that  the  marked  trees  were  the  two  end  trees  in  a  square  of  one 
hundred  trees.  In  addition  to  these  eight  trees,  two  trees  in  the 
middle  of  the  square  were  also  marked,  thus  completing  the  plot. 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA 


317 


Fig.  21. — Lisbon  lemon  tree  in  grove  heated  with  one  stove  per  tree,  crop 
and  tree  practically  uninjured.    Compare  fig.  20. 

This  plot  arrangement  is  illustrated  by  the  following  diagram : 
RECORD  PLOT  ARRANGEMENT 


1 

X 
X 
X 
X 
X 
X 
X 
X 

7 

o 

X 
X 
X 
X 
X 
X 
X 
X 

8 

X 
X 
X 
X 
X 
X 
X 
X 
X 
X 

X 
X 
X 
X 
X 
X 
X 
X 
X 
X 

X 
X 
X 
X 

5 

X 
X 
X 
X 
X 

X 
X 
X 
X 

(5 

X 
X 
X 
X 
X 

X 
X 
X 
X 
X 
X 
X 
X 
X 
X 

X 
X 
X 
X 
X 
X 
X 
X 
X 
X 

3 

X 
X 
X 
X 
X 
X 
X 
X 

9 

4 

X 
X 
X 
X 
X 
X 
X 
X 

10 

The  figures  in  the  diagram  represent  the  locations  of  trees  studied. 


318 


UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 


This  arrangement  eliminated  the  personal  equation  in  tree  selection, 
care  being  taken  that  the  trees  of  a  given  variety  were  of  the  same 
general  type.  Great  care  was  also  used  to  prevent  other  influences 
on  production  than  the  heating  methods  used  from  interfering  with 
the  results.  Naturally,  all  observable  influences  on  individual  tree- 
production  which  might  tend  to  interfere  with  the  results  or  modify 
them  were  considered  in  locating  the  plots.  From  our  experience 


Fig.  22. — The  effect  of  the  freeze  on  unheated  Eureka  lemon  tree.     Such 
trees  have  since   recovered,   but   two   years'   crops  were   lost. 

with  these  plots  since  their  selection,  we  feel  sure  that  the  results 
represent  fairly  the  influences  of  heating  as  compared  with  no  heating. 

The  crops  from  all  the  trees  were  picked  at  regular  intervals  for 
one  year.  After  completing  one  year's  data,  it  was  decided  that  it 
was  unnecessary  to  continue  records  in  all  of  the  plots  for  a  second 
year.  Two  plots,  one  heated  and  one  not  heated,  were  selected  for 
the  second  year's  data,  and  records  from  all  of  the  other  plots  were 
discontinued.  The  difference  in  production  between  the  heated  and 
unheated  plots  was  found  to  be  considerable  the  second  year. 

During  the  experiment  each  tree  was  picked  separately.  The  fruits 
were  sorted  into  four  grades — green,  tree-ripe,  frozen,  and  culls. 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  319 

After  sorting,  the  fruits  of  each  grade  were  counted  and  weighed. 
The  percentage  of  each  of  these  four  grades  of  fruit  produced  on  each 
plot  is  given  in  the  following  table,  and  is  self-explanatory. 

The  average  cost  of  heating  in  the  orchards  where  the  plots  were 
located  has  also  been  secured  from  records  kept  by  the  growers  for 
this  purpose. 

TABLE  15 

PERCENTAGES  OF  DIFFERENT  GRADES  OF  FRUIT  ON  EACH  PLOT. 
Figures  based  on  iveight  of  fruit  in  the  crop  of  the  year. 

LISBONS 
Heated  Plots  Unheated  Plots 

61.4% Green 19.2% 

26.5%..  Tree  Ripe ....  4.8% 

Plot  4     10.6%.  Frozen 74.3%   Plot  1 

1-6%...  Culls 1.6% 

74.4% Green 31.3% 

17.1% Tree  Ripe ....  1.6% 

Plot  6       6.5%                                         Frozen ..66.8%   Plot  8 

•2.1%.  Culls 0.2% 

57.2% Green .10.5% 

39.4%.  Tree  Ripe  6.1% 

Plot  9       1.6%.  .Frozen 83.2%   Plot  10 

1.9%  Culls 0.2% 

Average  of  the  three  series. 

64.3% Green 20.4% 

27.7%  .Tree  Ripe                     4.2% 

6.2%.  ..Frozen 74.8% 

1.9%.  Culls 0.7% 

EUREKAS 

Plot  7  Plot  5  Plot  3 

Well  heated  Poorly  heated  Unheated 

Green 50.7%  39.9%  32.3% 

Tree  Ripe.                                        43.2%  42.4%  7.3% 

Frozen 2.6%  14.1%  58.0% 

Culls...  3.5%  3.6%  2.4% 

UNHEATED  EUREKAS  vs  UNHEATED  LISBONS 
Unheated  Eurekas  Unheated  Lisbons 

32.3%.  ..Green..  49.5% 

7.3%  .Tree  Ripe  7.8% 

PlotS     58.0%  .Frozen .40.7%   Plot  2 

2.4%...  ..Culls .  2.1% 

Both  plot  3  and  plot  2  were  partially  protected  by  heaters  in  neighboring  groves 


320  UNIVERSITY  OP  CALIFORNIA — EXPERIMENT  STATION 

TABLE  16 
RETURNS  PER  ACRE,  F.O.B.  PACKING  HOUSE. 

LISBONS 
Heated  Plots  Unheated  Plots 

Plot  4  Plot  1 

$1759.59 $424.22 

Plot  6  Plot  8 

$888.00 $300.98 

Plot  9  Plot  10 

$2563.46 $128.15 

Average  of  the  three  series 
$1737.02 $284.45 

EUREKAS 

Plot  7  Plot  5  Plot  3 

Well  Heated  Poorly  Heated  Unheated 

$1423.06  $768.47  $352.54 

UNHEATED  EUREKAS  vs  UNHEATED  LISBONS 

Plot  3  Plot  2 

Unheated  Eurekas  Unheated  Lisbons 

$352.54  $1126.35 

Plots  3  and  2  were  partially  protected  by  heaters  in  neighboring  groves. 


TABLE  17 

AVERAGE  COST  OF  HEATING  PER  ACRE  ON  ALL  HEATED  PLOTS 
IN  THE  EXPERIMENTS 

Stoves 

Cost $53.29 

Interest..  3.20 


$56.49 

Depreciation,  33^% $18.78 

Reservoir  and  pipe  lines 

Cost $32.82 

Interest...  1.97 


$34.79 

Depreciation,  10% 3.48 

Oil  used 57.95 

Filling  pots,  lighting  and  refilling 21.09 

Total  average  cost  $101.30 


EFFECTS  OF  FREEZES  ON  CITRUS  IN  CALIFORNIA  321 

The  value  of  the  fruit  in  the  different  plots,  computed  to  the  acre 
basis,  was  secured  through  the  owners  of  the  orchards  who  furnished 
the  figures  of  the  actual  returns  for  this  fruit  during  the  period 
of  observation,  and  it,  together  with  the  average  cost  of  heating,  will 
be  found  summarized  in  tables  16  and  17. 

The  writers  do  not  believe  it  to  be  necessary  for  them  to  comment 
on  the  results,  as  the  tables  are  self-explanatory.  They  hope  that  it 
may  prove  to  be  of  some  value,  in  that  it  shows  the  actual  behavior 
of  heated  and  unheated  Eureka  and  Lisbon  lemon  trees  in  the  Corona 
district  for  the  year  following  the  freeze. 

The  observations  presented  here  were  made  possible  by  the  hearty 
co-operation  of  the  lemon  growers  owning  the  orchards  in  which 
experiment  plots  were  located.  All  of  the  expense  of  picking,  loss 
of  fruit  due  to  cutting,  information  as  to  cost  of  heating,  value  of 
crop,  and  other  factors  have  been  furnished  by  these  growers. 

The  writers'  only  concern  has  been  to  secure  reliable  data  to  add 
to  the  subject  of  the  practical  value  of  orchard  protection  as  a  whole. 


BULLETINS 

No.  No. 

230.   Enological  Investigations.  276. 

250.  The  Loquat.  277. 

251.  Utilization  of  the  Nitrogen  and  Organic  278. 

Matter   in    "Septic   and    Imhoff  Tank  279. 

Sludged.  280. 

252.  Deterioration  of  Lumber. 

253.  Irrigation   and  Soil   Conditions  in  the  281. 

Sierra  Nevada  Foothills,  California. 

255.  The  Citricola  Scale.  282. 
257.  New  Dosage  Tables. 

261.  Melaxuma    of    the    Walnut,    "Juglans  283. 

regia."  284. 

262.  Citrus   Diseases   of  Florida   and   Cuba  286. 

Compared  with  Those  of  California.  288. 

263.  Size  Grades  for  Ripe  Olives. 

264.  The  Calibration  of  the  Leakage  Meter.  290. 

265.  Cottony  Rot  of  Lemons  in  California. 

266.  A  Spotting  of  Citrus  Fruits  Due  to  the  291. 

Action  of  Oil  Liberated  from  the  Rind. 

267.  Experiments  with  Stocks  for  Citrus.  292. 

268.  Growing  and  Grafting  Olive  Seedlings. 

270.  A  Comparison  of  Annual  Cropping,  Bi-  293. 

ennial  Cropping,  and  Green  Manures  294. 

on  the  Yield  of  Wheat.  295. 

271.  Feeding  Dairy  Calves  in  California.  296. 

272.  Commercial  Fertilizers.  297. 

273.  Preliminary  Report  on  Kearney  Vine-  298. 

yard  Experimental  Drain.  299. 

274.  The  Common  Honey  Bee  as  an  Agent 

in  Prune  Pollination  300. 

275.  The  Cultivation  of  Belladonna  in  Cali-  301. 

fornia. 


The  Pomegranate. 

Sudan  Grass. 

Grain  Sorghums. 

Irrigation  of  Rice  in  California. 

Irrigation  of  Alfalfa  in  the  Sacramento 
Valley. 

Control  of  the  Pocket  Gophers  in  Cali- 
fornia. 

Trials  with  California  Silage  Crops  for 
Dairy  Cows. 

The  Olive  Insects  of  California. 

Irrigation  of  Alfalfa  in  Imperial  Valley. 

Commercial  Fertilizers. 

Potash  from  Tule  and  the  Fertilizer 
Value  of  Certain  Marsh  Plants. 

The  June  Drop  of  Washington  Navel 
Oranges. 

The  Common  Honey  Bee  as  an  Agent 
in  Prune  Pollination.  (2nd  report.) 

Green  Manure  Crops  in  Southern  Cali- 
fornia. 

Sweet  Sorghums  for  Forage. 

Bean  Culture  in  California. 

Fire  Protection  for  Grain  Fields. 

Topping  and  Pinching  Vines. 

The  Almond  in   California. 

The  Seedless  Raisin  Grapes. 

The  Use  of  Lumber  on  California 
Farms. 

Commercial  Fertilizers. 

California  State  Dairy  Cow  Competi- 
tion, 1916-18. 


CIRCULARS 

No.  No. 

113.  Correspondence  Courses  in  Agriculture.  165. 

114.  Increasing  the  Duty  of  Water. 

115.  Grafting  Vinifera  Vineyards.  166. 
124.  Alfalfa   Silage  for  Fattening  Steers.  367. 

126.  Spraying  for  the  Grape  Leaf  Hopper.  168. 

127.  House  Fumigation. 

128.  Insecticide  Formulas.  169. 

129.  The  Control  of  Citrus  Insects.  170. 
131.    Spraying  for  Control  of  Walnut  Aphis. 

138.   County  Farm  Adviser.  172. 

135.  Official  Tests  of  Dairy  Cows.  174. 

136.  Melilotus  Indica.  175. 

137.  Wood  Decay  in  Orchard  Trees. 

138.  The  Silo  in  California  Agriculture.  176. 

139.  The   Generation   of  Hydrocyanic   Acid 

Gas  in  Fumigation  by  Portable  Ma  177. 

chines.  179. 

140.  The  Practical  Application  of  Improved 

Methods  of  Fermentation  in  Califor-  181. 
nia  Wineries  during  1913  and  1014. 

142.  Practical  and  Inexpensive  Poultry  Ap-  182. 

pliances. 

143.  Control    of    Grasshoppers   in    Imperial  183. 

Valley.  184. 

144.  Oidium  or  Powderv  Mildew  of  the  Vine.  185. 

147.  Tomato  Growing  in  California. 

148.  "Lungworms."  186. 

150.  Round  Worms  in   Poultrv.  187. 

151.  Feeding  and  Management  of  Hogs.  188. 

152.  Some  Observations  on  the  Bulk  Hand-  189. 

ling  of  Grain  in  California.  191. 

153.  Announcement  of  the  California   State  192. 

Dairy  Cow  Competition,   1916-18.  193. 

154.  Irrigation   Practice   in    Growing   Small  196. 

Fruits  in  California.                                 %  197. 

155.  Bovine  Tuberculosis. 

156.  How  to  Operate  an  Incubator.  198. 

157.  Control  of  the  Pear  Scab.  199. 

158.  Home  and  Farm  Canning.  200. 

160.  Lettuce  Growing  in  California. 

161.  Potatoes  in   California.  ?01. 

162.  White    Diarrhoea    and    Coccidiosis    of  202. 

Chicks. 

164.   Small  Fruit  Culture  in  California.  203. 

204. 


Fundamentals  of  Sugar  Beets  under 
California  Conditions. 

The  County  Farm  Bureau. 

Feeding  Stuffs  of  Minor  Importance. 

Spraying  for  the  Control  of  Wild  Morn- 
ing-Glory within  the  Fog  Belt. 

The  1918  Grain  Crop. 

Fertilizing  California  Soils  for  the 
1918  Crop. 

Wheat  Culture. 

Farm  Drainage  Methods. 

Progress  Report  on  the  Marketing  and 
Distribution  of  Milk. 

Hog  Cholera  Prevention  and  the 
Se_rum  Treatment. 

Grain  Sorghums. 

Factors  of  Importance  in  Producing 
Milk  of  Low  Bacterial  Count. 

Control  of  the  California  Ground 
Squirrel. 

Extending  the  Area  of  Irrigated  Wheat 
in  California  for  1918. 

Infectious  Abortion  in  Cows. 

A  Flock  of  Sheep  on  the  Farm. 

Beekeeping  for  the  Fruit-Grower  and 
Small  Rancher,  or  Amateur. 

Poultry  on  the  Farm. 

Utilizing  the  Sorghums. 

Lambing  Sheds. 

Winter  Forage  Crops. 

Pruning  the  Seedless  Grapes. 

Cotton  in  the  San  Joaquin  Valley. 

A  Study  of  Farm  Labor  in  California. 

Dairy  Calves  for  Veal. 

Suggestions  for  Increasing  Egg  Pro- 
duction in  a  Time  of  High-Feed  Prices. 

Syrup  from  Sweet  Sorghum. 

Onion  Growing  in  California. 

Growing  the  Fall  or  Second  Crop  of 
Potatoes  in  California. 

Helpful  Hints  to  Hog  Raisers. 

County  Organization  for  Rural  Fire 
Control. 

Pp.it  ns  a  Manure  Substitute. 

Blackleg. 


DIVISION  OF  SUBTROPICAL  HORTICULTURE 

COLLEGE  OF  AGRICULTURE 

Dcouncv    PAIIFORNIA 


'ast  date  stampe 


(43  1158  00527  3361 


SB 

369 

W.38st 


UC  SOUTHERN  REGIONAL  UBRAW  FACILITY 

A     001  095  405 


